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INTRODUCTION

‘Always it is by bridges that we live.’

Philip Larkin, ‘Bridge for the Living’

From earliest times, mankind has built bridges, and still today bridge construction remains heroic, the most absolute expression of the beauty and excitement invoked by man-made constructions that are practical, functional, and fit for their purpose. Bridges that are leaps of faith and imagination, that pioneer new ideas and new materials, that appear both bold and minimal when set in the context of the raw natural power they seek to tame, are among the most moving objects ever made by man. They are an act of creation that challenge the gods, works that possess the very power of nature itself. They are objects in which beauty is the direct result of functional excellence, conceptual elegance and boldness of design and construction.

Like most people, I am addicted to bridges – to their raw, visceral punch, to their often astonishing scale and audacity, enthralled by their ability to transform a place and community and amazed by the way a bold bridge can make its mark on the landscape and in men’s minds, capture the imagination, engender pride and sense of identity and define a time and place. A great bridge – one that defies and tames nature – becomes almost in itself a supreme work of nature.

Bridges embody the essence of mankind’s structural ingenuity, they show how nature can be tamed by harnessing nature, how mighty chasms and roaring waters – the very embodiment of natural power and grandeur – can be spanned by utilizing the structural forces and principles inherent in nature; bridge design demonstrates – with startling and dramatic clarity – the structural potential of different materials and how these materials can be given added strength through design, through the use of forms that work in accordance with the structural laws of nature. For example, stone can be given additional load-bearing capacity and be used to bridge wider spans by being wrought to form well-calculated arches, and wood and metal can achieve great spans if used not as simple beams but when fabricated to form lattice-like, triangulated, trussed structures, where load-bearing capacity comes not through mass but from thoughtful engineering.

The most thrilling bridges are, in many ways, those not enhanced by superficial or extraneous ornament or cultural references. What moves and impresses is their honest expression of the materials and means of construction – their only ornament is a direct result of the way in which they are built and perform. A great bridge has an emotional impact, it has a sublime quality and a heroic beauty that moves even those who are not accustomed to having their senses inflamed by the visual arts.

Bridges are a great paradox, they not only use nature against nature, but magically the best examples do not defeat or damage nature but enhance it, and, in ways that are sometimes hard to fathom, achieve a deep harmony with their surroundings. For these reasons bridges have captured the imagination of people through the ages and now they are the only large-scale and radical examples of modern design and construction that the public generally applaud. All can see that bridges stand for something most significant, for the indomitable human spirit, the love of daring and of challenge, the power of invention.

Bridges, of course, inhabit worlds way beyond the merely physical and visual. Having excited human imagination they have, for centuries, possessed a powerful symbolism. They have been seen as links between this world and the next, as symbols of transition, and as metaphors for life and death on earth, and of the journey of the soul to the afterlife – the means of crossing the great divide. This symbolism and fancy have, occasionally, been reinforced by fact, for some bridges have, quite literally and rivetingly, been bridges between worlds and have possessed almost more meaning than physical substance. For example, the stone-arched Bridge of Sighs in Venice, built in 1602 by Antonio Contino (who had earlier worked for his uncle Antonio da Ponte on the Rialto Bridge, see page 158) that formed a covered way between the interrogation rooms in the Doge’s Palace and the adjoining prison. It has long been assumed that the small windows in the bridge offered convicted prisoners their last view of Venice or of life. The idea of the bridge as a metaphor for transition or for a journey of the spirit seems universal. In fifteenth century Peru, the Inca saw the rainbow as a bridge between their homeland and heaven, while some of the indigenous people of Australia conceive of the link between worlds taking the form of the vast, arching and bridging body of the rainbow serpent, a creature as it happens that is most similar to the Lebe snake, the bridge-like ancestor of the Dogon people of Mali, Africa.

The Zhaozhou or Anji Bridge, Hebei province, China, completed in AD 605: an object in which form is dictated by function to achieve beauty and eternal elegance.

Detail of one of the arched and open spandrels of the Zhaozhou or Anji Bridge. This is the world’s oldest surviving open-spandrel, segmental arched bridge built in stone. The joints between the masonry blocks forming the arches are reinforced by wrought-iron bars or cramps.

For all these reasons bridges have been applauded as heroic, sacred – almost mystic – works by all cultures. Bridges of great scale or span were venerated in Medieval Europe, either as pious works that glorified God or as almost impossible acts of daring that could only have been achieved with the aid of the Devil (see page 94). Great bridges were, people assumed, creations that could only be completed through prayer and divine guidance or by the sale of the soul to dark forces. They were places where you could meet angels and saints as if conducting you to Heaven, or the Devil himself collecting his toll. Similarly in China: the truly remarkable Zhaozhou or Anji Bridge in Hebei province, built between 595 and 605 AD to the designs of Li Chun and the world’s oldest open-spandrel segmental arched masonry bridge, is particularly rich in myth, legend and stories of the supernatural. This is mainly because its construction methods and ambitious scale – its main arch of segmental forms spans a mighty 37.7 metres – astonished most contemporary observers. Li Chun achieved the wide span of the bridge by using 28 parallel and abutting arches, each formed with massive, precisely cut and wedged limestone voussoirs whose joints were strengthened with wrought-iron cramps or bars. The arch-topped open spandrels not only reduce the weight of the bridge without weakening it but also – by creating additional openings through its body – protect the bridge from being washed away by the force of unusually high and powerful flood waters. These novel design features and construction techniques gave the bridge great strength but also the flexibility necessary to withstand earthquakes.¹

Li Chun – clearly a man of advanced practical know-how – was himself not ignorant of the worlds of magic and of the spirits. The bridge is of pure, simple and practical design yet the keystones at the crown of the main arch are embellished with carvings that show the leering and horned heads of the Taotie motif. These beings from the spirit world were intended to protect the bridge from floods and from the potentially malevolent spirits of the river that might resent the bridge, for it robbed them of some of their power over those mortals who wanted to cross the water. In a Taoist culture, where all is animated and nature is seen as the great guide and inspiration, everything is alive – not just the river but the stones from which the bridge is made and, indeed, the bridge itself.

One legend about the bridge is like those attached to many European medieval bridges of prodigious span or slender form: it was constructed by an inspired human, in this case the fifth century BC engineer and philosopher Lu Ban, working with the aid of spirits. Another legend is that two Taoist Immortals – perfected beings who are masters of time and space and travel between the earth and the distant stars – decided to test the strength of this unprecedented bridge by thundering across it in tandem. The bridge survived this ordeal just as it survived resentful water spirits and – perhaps more impressively – earthquakes and centuries of neglect. It still stands, still does the job for which it was built 1,400 years ago, and continues to inspire and astonish – a thing of perpetual delight and timeless beauty that contrives, despite all it has seen and suffered, to look eternally youthful and modern.

The Humber Bridge, linking Yorkshire to Lincolnshire, was opened in 1981, and was seen by the poet Philip Larkin as a great symbol of human existence. ‘Always’, he observed, ‘it is by bridges that we live’.

THE ART OF BRIDGES

Always bridges have been seen as things of breathtaking, elemental beauty, as audacious and epic engines of transformation. The profound role that bridges play, in all their symbolical and metaphoric richness, in our imaginations is revealed – and confirmed – by the works of poets, painters and writers. Shortly before the Humber Bridge in England opened in 1981 – a huge and daring suspension bridge whose span of 1,410 metres was until 1997 the widest in the world – Philip Larkin wrote a poem about the arrival of this new creation near his home town of Kingston-upon-Hull. For the first time ever, the mighty Humber Estuary, dividing those on its Lincolnshire south bank from the natives of Yorkshire on the opposite bank and defining the character of the area, had been bridged. Larkin pondered on the way the bridge transformed the landscape and communities and promised new life to all the area – even, as it were, to the dead: ‘Lost centuries of local lives that rose…Seem now to reassemble and unclose, All resurrected in the single span’. Larkin also saw the bridge – the act of bridging – as a great symbol of human existence, of the transition from the past to the present, from life to death and to rebirth: ‘Always it is by bridges that we live’.²

Larkin, although suspicious of change, clearly had a guarded enthusiasm for such bridges. So it is perhaps slightly disappointing that this particular great engine of transformation has never quite lived up to its promise and proposed purpose. The bridge remains magnificent and sound but not used by the numbers that were anticipated. The communities on each side of the Humber have not embraced the opportunity to mix quite as fully as Larkin and the bridge builders imagined. So in this case the bridge has taken on another symbolism, one somewhat removed from that envisioned by Larkin – and has become the personification of the ancient Greek concept of hubris, the excessive pride and daring arrogance that leads man to defy the gods, and by so doing, create the implacable mechanism of his own downfall.

Many painters, for reasons never fully explained, have not only included bridges in their works as seemingly peripheral objects, but have at times become obsessed by them, or by their apparent meanings. Indeed, for some artists, bridges have become veritable muses, objects that unleash the creative force of the imagination. In the romantically rude but also idyllic landscape that enfolds behind the Mona Lisa there is a bridge. It has several arches that appear semi-circular in form. It could be Roman. Why did Leonardo da Vinci include a bridge in this particular portrait? There are any number of possible answers, the least acceptable of which is that he was merely reproducing a landscape and details with which he was familiar, painting what he saw. The pioneering technique he used to render the landscape – depth is implied by the use of paler, misty-looking colours and by a softening of detail – gives all a naturalism and realism. But this is clearly a fictitious and unreal landscape and one pregnant with deep meaning – but what meaning?

Whatever the meaning, it matured over the years. Leonardo started the work in 1503 and seems to have taken around fifteen years to complete it, mulling over it, carrying it with him into France, putting it aside, then taking it up. It was his shadow, a thing haunting him. Is it really just a portrait of ma donna – my lady – or m’onna Lisa, the wife of the wealthy Florentine silk merchant Francesco del Giocondo? Perhaps, but also – in certain ways – it is surely more. The time and care indulged means that, among other things, the Mona Lisa is a self portrait of the painter’s soul. His soul, with a bridge nearby. As well as being a painter, Leonardo was an inventor of technically advanced machines, an architect and a military engineer. Without doubt he knew much about bridges and almost certainly loved them for their structural logic and power. He probably also saw them as emblems of human achievement, as Humanist creations that reveal the dignity, value, ingenuity and intrinsic worth of man. Even without reference to God, man was confirmed in his high status by such acts of genius and endeavour as bridge construction.

Bridges appear in the paintings of Botticelli, Raphael and, in particular, in the work of Canaletto. He paints not just bridges in Venice but also, in the mid 1740s, in London. The wonder-bridge at the time was Westminster Bridge – the first major bridge over the Thames built since London Bridge was completed in the very early thirteenth century (see page 16). The new bridge had inspired London-based artists from the moment construction started in 1739 on the designs of the Swiss engineer, Charles Labelye. Richard Wilson had, in 1744, painted its arches rising from the water. When Canaletto painted the bridge in 1746, he placed it in an almost Venetian context – showing the river packed with boats and large ornamental barges – and also produced a remarkable view of London framed by one of the arches of the bridge, complete with timber centering still in place.

This playful and inventive work by Canaletto seems to have challenged – and inspired – the London-based artist Samuel Scott who around 1750, when the bridge was nearing completion, produced an almost obsessive series of paintings. He portrayed the bridge in its setting and, more remarkably, produced over half a dozen studies showing details of, and views through, a couple of arches. Scott was evidently determined to out-do Canaletto at his own game, for not only did he emulate Canaletto’s unusual arch-framed view of the city but also embellished his images of the bridge with the trappings of daily life. Scott placed bustling or pondering people on the bridge and showed construction details – it was to be an emblem of urban vitality, of change, of London, and a vehicle for grasping new and unexpected views of the city.

In fact this was another favoured symbolic role for the bridge – an elevated and disinterested platform from which to see the world in revealing perspective, as if an Olympian god were looking down on the world of mortals. In September 1802 this was precisely the lofty position that inspired William Wordsworth – who was in fact given extra elevation by being perched on top of a stagecoach – when he wrote Upon Westminster Bridge. Apart from the reference in the title, the poem doesn’t mention Westminster Bridge directly but it is obvious that without the bridge – without the experience of passing over water atop a slowly moving vehicle on a still, late summer morning – nothing would have been possible, no insights or pleasures gained. Moved by the view of the metropolis offered by this relatively new vantage point, Wordsworth had a sudden vision of urban beauty and, in homage, created a hymn to London: ‘Earth has not any thing to show more fair…The City now doth, like a garment, wear/ The beauty of the morning: silent bare…Ne’er saw I, never felt, a calm so deep!/ The river glideth at his own sweet will:/ Dear God! The very houses seem asleep;/ And all that mighty heart is lying still!’³

One of a series of paintings by Samuel Scott showing Westminster Bridge under construction in around 1750.

As artistically ecstatic are the paintings by Pierre-Auguste Renoir and Claude Monet. Paris’s oldest surviving bridge – the Pont Neuf completed in 1609 – and the life it engendered over the reflective river inspired Renoir in the early 1870s to help forge the fleeting light effects and immediacy of Impressionism. A few years later Monet became entranced by the little Chinese-style timber bridge he had created in the early 1880s within his garden at Giverny, France, and painted it in different lights to create a series of studies that in a sense define his art.

For both these artists bridges were clearly admirable things, just as they were a few years later for Surrealist and Dadaist artist Marcel Duchamp. In 1917, when defending his decision to display a urinal as a work of art in a New York gallery, Duchamp explained that by placing the urinal at an unusual angle, in the novel context of an art gallery, and naming it ‘Fountain’, its familiar ‘significance disappeared under a new title and point of view’. Duchamp claimed to have transformed the essence of the object in an almost alchemical manner by creating ‘a new thought’ for it in the eyes of the viewer. He’d opened, in the prophetic words of William Blake, new ‘doors of perception’.⁴ And to those who argued that to display such a piece of off-the-peg plumbing as a urinal was just plain vulgar and could not possibly be art, Duchamp simply replied: ‘that is absurd. The only works of art America has given are her plumbing and her bridges’.⁵

It is not just poets and painters who have viewed bridges as potent symbols and metaphors. So have novelists. For example Thornton Wilder, in The Bridge of San Luis Rey, published in 1927, uses the sudden collapse of an ancient, creeper-built suspension bridge in Peru in which five people are killed, to explore the nature of God and religion. The fate of the bridge becomes a metaphor for the fate of man, a symbol of divine will. Were the deaths merely random, revealing that God has no plan and ultimately that life is arbitrary or was the bridge’s collapse the long-ordained and deserved termination of the lives it took?

Claude Monet was inspired in the 1880s to produce numerous versions of the play of light on the Chinese-style bridge in his garden at Giverny.

BRIDGES OF DEATH AND REDEMPTION

Perhaps the most relentless literary pursuit of the bridge as symbol is Ivo Andric’s The Bridge on the Drina, a novel published in 1945 and inspired by Bosnia’s history and quest for independence and identity. The novel focuses on the town of Višegrad and the Mehmed Paša Sokolovi Bridge over the Drina river and spans 400 years from the time the region, town and river were dominated first by the Muslim Ottoman Turks and then by the Christian Austro-Hungarian Empire. It chronicles the religious battles between the communities that co-existed in a border town on a river forming a frontier between different peoples – and the thread that holds the narrative together and that weaves through time is the bridge.

In the novel – and in reality – the bridge is a mighty work. The Ottomans were skilled and prodigious bridge builders who, like the Romans before them, understood that bridges and roads were the means of expanding, holding and controlling a sprawling empire and of linking and unifying the diverse peoples that it contained. The Mehmed Paša Sokolovi Bridge was completed in 1577 to the designs of the Ottoman court architect Mimar Sinan on the orders of the Grand Vizier of Bosnia. Sinan was the greatest architect of the Golden Age of Ottoman power, the designer of the spectacular mid-sixteenth century Süleymaniye Mosque complex in Istanbul that remains an exemplary essay in the creation of an Islamic paradise on earth.

Sinan’s bridge over the Drina was nobly conceived – it was to measure 180 metres and cross the water by means of eleven stone-built pointed arches, each with spans of between 11 and 15 metres. In the novel, the Vizier had, as a boy, been kidnapped into slavery in Bosnia and resolved to build a bridge at Višegrad to purge his memories of initiation into slavery aboard a boat while crossing the Drina. The tale woven around fact tells of the harsh conditions and chaos of the initial phases of construction – marked by episodes of gruesome cruelty – gradually giving way to order, to harmony, and to final completion when the bridge becomes a source of pride and prosperity for Muslims and Christians alike.

The bridge, with its mid-span meeting place, assumed the symbolic – in many ways actual – role of town centre and focus of activities that gave the community identity and cohesion. Then decline sets in, the bridge loses its importance as a trade route and finally – in the novel and in reality – soon after the start of the First World War ceased to exist as any sort of route at all because retreating Austrian forces blew up a number of its arches as the enemy approached. As Andrew Saint has observed of the way the bridge is presented in this novel: ‘Here is an engineer’s story, [it is] about courage, effort and technique; about the benefits a magnificent and useful monument can confer across generations; about amazement at its construction and pride in its endurance’.⁶ He could have added that the story also talks of the way bridges can bring prosperity and unite communities.

The real-life story of the bridge across the Drina after the publication of the novel (that in 1961 won the Nobel prize for literature) has bizarre and brutal twists worthy of the darker moments of Andric’s imagination. The three arches destroyed in the First World War were repaired, as were the five subsequently destroyed in the Second World War and by the 1990s the bridge was regarded as a major historic and architectural monument of Yugoslavia. Then descended the dark and ancient shadow of hatred and cruelty. There was division, fragmentation, a return to religious war, the imposition of the ghastly mechanisms of ‘ethnic cleansing’ and land appropriation by the most violent means imaginable. In 1992 a large group of local Muslims were herded to the centre of the bridge – to the place of creative and convivial gatherings in Andric’s vision of the history of the bridge – and then flung off ‘and shot at for sport by Serbs as they fell’.⁷ The bridge, now again a place of calm and beauty but more than ever haunted, currently belongs to the Republic of Serbia. Few visit it: the suffering it has seen is too great for most to bear.

One bridge nearby, with a comparable history and story, I have explored in detail. The bridge at Mostar was completed in 1566 and with a single and elegant stone arch spanning 29 metres and rising 19 metres above the water, is one of the great engineering marvels of the Ottoman empire – a testimony to the taste, culture and scientific skills of the Muslim world that created it. The construction technique was ingenious – the limestone blocks were finely cut and their joints strengthened by the use of wrought iron pins, set in lead to prevent them rusting, expanding and cracking the stone. As in Andric’s story of the bridge at Drina, the bridge at Mostar – with what many at the time believed was the longest stone-built arched span in the world – became a great source of local pride and brought prosperity and distinction to the town. It also became the focus of customs and rituals – notably offering young Mostar males of all persuasions the opportunity to publicly demonstrate their virility to all who might be interested by leaping from the crown of the bridge into the generally shallow water below.

The history, beauty and technical excellence of this bridge proved its undoing. The same vicious conflict following the break-up of Yugoslavia that led to the deaths on the bridge across the Drina also engulfed Mostar. The town had a complex and mixed community – Orthodox Christian Bosnian Serbs, Slavic Muslims and Roman Catholic Croats – and in mid 1992 this long stable but potentially volatile community fragmented. Fighting flared on opposite sides of the bridge, each the territory of neighbours now in conflict. Outside forces arrived and the bridge became a target – this was culture very much in the firing line. The bridge was obviously of military and strategic significance in the fighting – but it was also a symbol, an emblem of Muslim presence, of Islamic culture. As such some of the fighting factions found it intolerable. Despite attacks, the bridge managed to survive until November 1993 when Croat forces finally shelled it to destruction.

When the fighting gradually died down, and Mostar found itself stabilized as part of Bosnia and Herzegovina, it was resolved that this cultural wonder must be rebuilt. This was not only to reclaim lost beauty and history, but was to be an act of reconciliation that would give Mostar back its heart, its identity and its role as a trading centre. The European Union got involved, money was made available by various states and an exemplary reconstruction took place utilizing as many of the old stones as possible and using traditional building materials and techniques. By July 2004 the great wrong had been put right and the noble bridge rebuilt. I saw it a few months later. It looked superb, as if the last ten years had never been. Mostar has its wonderful bridge back, the ancient trade routes are reconnected, and customs revived. Even while I was there muscular young men were gaily tossing themselves off the top of the arch to splash into the water far below. But near the bridge I spied a stone standing against a wall, and on the stone was written, ‘Don’t forget’. The stark and powerful words provoked memories of ancient, prophetic texts, especially those touching on mortality and transience. I looked up the famous lines from the eleventh century Rubaiyat of Omar Khayyam: ‘The moving finger writes: and, having writ, moves on: nor all your piety nor wit shall lure it back to cancel half a line. Nor all your tears wash out a word of it’.⁸ Yes indeed, we are ‘weighed in the balance, and…found wanting’ (Daniel, 5:27). A bridge, for all its engineering wonder and potential symbolism, is in many ways just a bridge, a physical fact. The sign near the bridge at Mostar, I suppose, is saying that some things when lost cannot be found, that it is easier to mend a broken bridge than it is a broken heart.

Mostar, Bosnia and Herzegovina, in November 2004. The beautiful mid-sixteenth century bridge had recently been reconstructed after its destruction in 1993, but the words written on a stone nearby – ‘Don’t Forget’ – were a reminder that the intense emotions that had been aroused by the destruction of the bridge (a symbol of Muslim culture as well as a military target) – had not been fully pacified by its rebuilding.

The bridges at Višegrad and Mostar have, by turn, been symbols of identity, despair, death and redemption. Other bridges have not had such emotional, roller coaster rides but, nevertheless, have still enjoyed extraordinary existences that have made them central to the life of their city or nation and so much more than just routes of communication or means of crossing a great divide. The Széchenyi chain bridge in Budapest, stretching 375 meters across the Danube and completed in 1849, launched the fortunes of the city and has become a symbol of Hungarian pride and liberty (see page 245). Similarly, although for differing reasons, the Brooklyn Bridge in New York (see page 284), the Sydney Harbour Bridge (see page 218), and the Golden Gate Bridge in San Francisco (see page 228) have all become the much-loved emblems of the cities in which they stand. These were all, in their time and in their different ways, bold technical pioneers and creations of epic scale and ambition. But earlier ages have also produced bridges with comparable emotional punch. There were the paradise bridges of Persia (see page 118), the great pious works of medieval France, such as the bridges at Avignon and Orléans (see pages 92 and 82), and of central Europe.

THE ALCHEMICAL BRIDGE

The Charles Bridge in Prague, the Czech Republic, is perhaps the best-known man-made object in a city packed with architectural wonders. The bridge has an extraordinary life and history, and a great importance. When completed in the very early fifteenth century the 516-metre-long, stone-built, sixteen-arch bridge not only connected the two halves of the city in spectacular style (an earlier ramshackle affair had been swept away in the 1340s) but also, as the only route across the mighty river Moldau (Vltava) formed a vital trade route that – almost literally – connected Europe to the east. It was – in fact as well as fancy – a bridge between worlds, with both its ends secured by robust guard towers.

The importance of the bridge was recognized from the moment construction started. The foundation stone was laid in 1357 with, it is alleged, the Emperor Charles IV insisting that the event take place at 5.31 am on 9 July. Royal astronomers, mathematicians and those learned men consulted had, apparently, ordained that this moment was auspicious because it enshrined a palindrome comprising all the odd numbers 1-3-5-7-9-7-5-3-1. A palindrome is a sequence of numerals or letters – sometimes arranged in a ‘magic square’ – that either reads the same from different directions or possesses different meanings or pronunciations when read from different direction. For example, ‘a man, a plan, a canal, Panama’ has the same letters from either direction but is not pronounced the same from either direction – to grasp the point try saying ‘amanap lanac a nalp a nam a’.

Medieval Prague was indeed a meeting place of east and west, a melting pot of different cultures and religions. It had a large Jewish community from as early as the tenth century but this suffered waves of persecution culminating in the late twelfth century with an obligation imposed on all Jews to settle in an enclave on the east bank of the Moldau, near the main city square – and thus was created the first Jewish Ghetto. In the mid fourteenth century Charles IV relinquished some of the state power of the Jewish community, and perhaps even consulted rabbis about the construction of the bridge. These men would undoubtedly have enshrined the ancient esoteric wisdom of the Kabbalah, the branch of mystic Judaism devoted to the quest for the origin of life, of creation, and of the nature of the relation between God and man.

A key part of this quest – the code that could explain all – was language itself, in particular the twenty-two ‘foundation letters’ of the Hebrew alphabet which Kabbalists believed was the creation and direct gift of God and pregnant with many layers of meaning. One of the most important Kabbalistic texts – the 2,000 year old Sepher Yetzirah or Book of Creation – states most directly that God ‘ordained’ the letters of the alphabet: ‘He hewed them, He combined them, He weighed them, He interchanged them. And He created with them the whole creation and everything to be created in the future’. So if Kabbalistic rabbis were involved with the ritual of the foundation of the bridge, then the ceremony was evidently of a deeply mysterious nature, akin to casting a spell. This was the age of alchemy and of miraculous transformation, of the quest for the Philosopher’s Stone, the ‘elixir of life’ and of attempts to transmute base matter into fine, the material into the spiritual. The construction site of the bridge could have been seen as a vast alchemical laboratory, for bridges are, in their way, a form of alchemy – they transform, they bring life. As Philip Larkin wrote in 1981: ‘All will be ‘resurrected in the single span’.⁹

A significant clue to the meaning of the foundation ceremony, and to the power of the Kabbalah in fourteenth-century Prague, lies in the story of one of the most remarkable alleged inhabitants of the medieval city – the golem. This is a creature of Jewish legend that – like Adam – is made of mud, but animated by man not God. In consequence the golem was a parody of divine creation, a mere perverse shadow of humanity, lacking a soul but desiring one and given to hubristic displays leading to chaos and, eventually, self destruction. The golem is mentioned in the Talmud and implied in several Old Testament texts, notably Psalm 139:14-16. Here, in most mystic fashion, a being seemingly full of pride addresses God and says: ‘I will praise thee; for I am fearfully and wonderfully made…My substance was not hid from thee, when I was made in secret, and curiously wrought in the lowest parts of the earth. Thine eyes did see my substance, yet being unperfect; and in thy book all my members were written, which in continuance were fashioned’. An ‘unperfect’ or unshaped substance in Yiddish is ‘goylem’.

The Charles Bridge in Prague was started in 1357 and its fine array of Baroque religious statues was added from the 1680s, turning a stroll across the bridge into a virtual Roman Catholic pilgrimage.

The means of animation was by tradition a deep and closely guarded secret but involved the Kabbalah and the use of certain letters from the Hebrew alphabet and magic words from, no doubt, the ‘book’ in which all about the golem was ‘written’. To deactivate his creation the magician, for such he was, had to remove letters from words to transform their meaning. For example, one legend says, that to bring the golem to life the word ‘truth’ has to be written in Hebrew on its forehead, and to kill it a letter has to be removed from that word that changes its meaning from ‘truth’ to ‘death’. Or to kill the golem the magician had to pronounce the animating word – the magic palindrome – backwards.

For reasons now lost in myth, the golem became closely associated with Prague and, in legend, was created and animated by rabbis as a means of protecting the inhabitants of the ghetto from anti-Semitic attacks. In the early nineteenth century the writer Berthold Auerbach went so far as to identify the learned late-sixteenth-century Prague rabbi Judah Loew ben Bezalel as the creator of a golem. Interesting, at this very time, the emperor Rudolf II gave active encouragement to alchemists at his court in Prague as they pursued their various vital and curious quests.

Given all this, and assuming some mystic intent, it must be assumed that the palindromic foundation time and date was intended to give the bridge some special quality – to protect it presumably, but perhaps even animate it in some way. And there is another peculiarity about the bridge. Legend says eggs were mixed into the mortar used to bind the stone and recent analysis suggests the old mortar does indeed contain some unusual organic matter.

Why eggs? Well, it is possible that their addition hardened or improved the mortar in some practical manner. But also, of course, eggs are pretty universally regarded as emblems of life, virility, of creation – especially, as it happens, in Islam where mosques often contain an ostrich egg. I remember seeing – to my surprise – a couple perched on the roof of the massive mud-built mosque in Djenne, Mali. The 79th sura, or chapter, of the Koran explains all. This sura – entitled rather intriguingly ‘The Soul Snatchers’ – starts by warning that the hearts of all humanity – including ‘those who snatch away men’s souls’ – will ‘on the day the Trumpet sounds its first and second blast…be filled with terror’. The sura then goes on to discuss creation and states that God ‘spread the earth, and, drawing water from its depth, brought forth its pastures’. This is one English translation of the seventh century Arabic of the original text.¹⁰ Other English translations use slightly different words, but in the original Arabic text is the word ‘daha’, which can be taken to mean an elliptical, geoid or, indeed, an ostrich-egg shape. Did the Arabs of the seventh century really know, as suggested through the revelation of the Koran, that the world was of spherical form? This would be an extraordinary insight for the time and is one that current Islamic scholars use to support their argument that the Koran is truly the word of God, for in the seventh century only He knew the shape of the world.

‘Assuming some mystic intent...the palindromic foundation time and date was intended to give the bridge some special quality – to protect it presumably, but perhaps even animate it in some way.’

So eggs had huge and ancient symbolic meaning in the fourteenth century, particularly in those countries of central Europe relatively close to the borders with Islam and familiar with its religious beliefs and customs. Were they added to the material body of the Charles Bridge – originally called simply the Stone Bridge – as part of some magic or religious ritual to quicken it? This is perhaps not as odd as it sounds. Stone has been venerated by different peoples and religions throughout time. The Ka’ba in Mecca – the holiest place in Islam – enshrines a stone, now called ‘the Black Stone’, that is perhaps a meteorite. In Islamic belief the stone fell from heaven – a gift of God – for Adam and Eve to use as an altar and was later used by Abraham. Whatever the truth, this stone was an ancient sacred object well before the rise of Islam. The Dome of the Rock on the Temple Mount in Jerusalem covers a pinnacle of stone held sacred by both Muslims and Jews because they believe it to be both the rock on which Abraham proposed to sacrifice Isaac, and the veritable Foundation Stone of God’s creation mentioned in the Book of Isaiah where God says: ‘…Behold, I lay in Zion for a foundation a stone…a precious corner stone, a sure foundation’. (Isaiah 28:16).

When Jews pray towards the west or ‘Wailing’ wall of the Temple they are in fact facing the buried body of the stone that peeps above the surface within the Dome of the Rock. They are praying towards what many believe to be Mount Moriah, now embraced by the Temple Mount and which, as the place where all things started, bears, as it were, the direct traces of God’s presence. And for Christians, rocks are an ever-present imagery (see page 91). Christ told Peter that he was his ‘rock’ upon which he would build his church (Matthew 16:18) and referred to himself as the ‘stone which the builders rejected’ – prophesized in the 118th Psalm – that would ‘become the head of the corner’ – which is to say the foundation stone of the church of redemption, (Matthew 12:10).

Whatever the intention behind the bridge’s foundation rituals, as it turned out, they brought no good to the Jews of Prague. During Easter 1389, as the bridge was nearing completion, the clergy in the city inflamed the latent anti-Semitic feelings of the population by announcing that Jews – long held responsible by Christians for the death of Christ – had desecrated the host, the Eucharistic wafer that becomes the body of Christ during the mystery of the Roman Catholic Mass. Murderous chaos followed which resulted in the Jewish ghetto being pillaged and burnt, and much of the Jewish population of Prague – estimated at around 3,000 people – being murdered.

Four years later the bridge – still incomplete – became itself the focus of a grim event that, in later centuries, did much to define the character and spiritual aspirations of the city. On the night of 20 March 1393, John Nepomuk was killed by being thrown from the bridge on the orders of Wenceslaus, King of Bohemia, who in 1378 succeeded his father, Charles IV, as ruler of Prague. Nepomuk was a principled cleric who displeased Wenceslaus by refusing to divulge to him the secrets of his Queen’s confession. In consequence Nepomuk was tortured (apparently his tongue was removed in no uncertain manner) before being tossed from the Charles Bridge. His sufferings and manner of martyrdom led Nepomuk to be canonized, made the patron saint of Prague, the official holy protector against floods, and inspired within Bohemian architects for years to come a morbid interest in tongues. As motifs, as plan forms or vault patterns, stylized tongues, small or vast in scale, enliven the sacred architecture of the region.

The Charles Bridge stood firm and largely unaltered for nearly 300 years, maintained by a toll collected by the crusading military order of the Knights of the Red Cross and Star whose mother-house was located next to the bridge. Then, in the 1680s, the bridge’s lurid past caught up with it. This was a time of Roman Catholic resurgence in Bohemia, following the dramatic defeat in 1620 of Protestant forces at the Battle of the White Mountain, and if the bridge’s foundation had anything to do with the ancient arts of magic, alchemy or the Kabbalah, then the Catholics felt something had to be done about it. And it was. From 1683 until about 1714, the bridge’s parapets were loaded with statues carved of stone, mostly of saints and clerics – including, of course, an image of St John Nepomuk. The bridge was turned into a Roman Catholic shrine – walking along it became a mini-pilgrimage – with the flamboyantly posturing parade of saints, carved in ostentatious baroque manner, being a tremendous late flowering – in theology and in art – of the Counter Reformation. Virtually every one of these statues has now gone, their weathered and battered hulks carted off to the Lapidarium museum and replaced by replicas. But the fourteenth century bridge endures, a tribute to its robust construction, to the skill of the master mason Peter Parler who supervised building works and – perhaps – to the strange ritual of its foundation.

STRUCTURAL PRINCIPLES

During the late fourteenth century in Europe, when the Charles Bridge was being built, the technical approach to bridge building was starting to change. Masons like Peter Parler tended to have an almost intuitive understanding – honed by years of experience and exposure to the trade ‘mysteries’ of their craft – of the structural forces engaged in bridge construction. Their responses to these forces of nature, and to the manner in which loads are contained or transmitted by structures of different forms or materials, were usually pragmatic and the result of empirical observation, practical experiment and trial and error. This resulted in safe and conservative designs with few great and dramatic leaps forward – which is what makes the unusually wide-span elliptical arches of the mid fourteenth century Ponte Vecchio in Florence so novel and interesting (see page 150). Throughout the fifteenth century things started to change, gradually at first, as bridge building became more theoretical and finely calculated. But it was not until the late sixteenth century that scientific understanding of the theory of bridge construction started to dominate the business of bridge building.

Crucial to this new understanding was the ground-breaking research and analysis undertaken in the late sixteenth and early seventeenth centuries by mathematician, astronomer and philosopher Galileo Galilei. This allowed late Renaissance engineers to calculate the ways in which the shape and size of structural members – for example beams and trusses – and the materials from which they were made would affect their ability to carry and transmit loads. Significantly Galileo identified the ‘scaling problem’. He established the principle that as a beam increases in length it decreases in strength, unless its thickness and breadth increase disproportionately. He also demonstrated that this escalation of scale has very definite limits dictated by nature. Quite simply, if a beam is increased in scale beyond a natural limit it will be capable of supporting no loads at all and break under its own weight.

In the late sixteenth century the scientific and mathematical approach to construction was in fact being explored by many and evolved at a rapid rate. For example, the architect Andrea Palladio’s Quattro Libri dell’Architettura of 1570 included the first published illustration of a triangulated truss – a robust structure for transferring loads through a rigid system of triangular forms. Other important publications pioneering, promoting or explaining theories of bridge construction included Machinae Novae of 1595 by Fausto Veranzio, which includes information on tied-arch bridge construction, the oval lenticular or lentil-shaped truss, and the iron chain-link suspension bridge. A key later work containing much technical information is Traitre des Ponts of 1716 by Hubert (Henri) Gautier.

BRIDGE DESIGN AND CONSTRUCTION

The permutations of materials and structural principles employed in bridge construction are seemingly many, varied and complex – timber, brick, stone, cast and wrought iron, steel, hydraulic cement, mass concrete and steel-reinforced concrete, arches of diverse form, beams, cantilevers, pylons, cables and masts. But in its aim bridge construction is straightforward and construction simple. The object is to link two points of land as safely and efficiently as possible. If the obstacle being bridged is running water, then the ideal is to achieve wide spans with minimal support rising from the water to make the bridge easier to build and maintain, to avoid disturbing navigation, and to reduce the risk of the bridge being swept away.

In essence bridge construction is of two basic types. The carriageway – be it for vehicles or pedestrians – is either supported from below or suspended from above. If the ‘dead’ load of the carriageway (its weight) and the ‘live’ load of the carriageway (the weight of the use it carries plus the ‘environmental load’ comprising the weight and pressure of rain, snow and wind) are supported from below it must be carried on arches or vaults of varied types; on beams either cantilevered from, or supported by, abutments and piers; or set within a lattice-like engineered truss wrought of timber or metal. There are two models of nature for support from below: rock formations that arch over; and timber logs or beams laid across, chasms or rivers.

If the ‘dead’ and ‘live’ loads are supported from above, the carriageway must be suspended from well-anchored cables or chains stretching over masts to form inverted arches of strong catenary shape, or from natural features – a system known in China from the second century BC. Cables can also be stayed or anchored firmly to a single support to create a cable-stayed bridge. The prototype in nature for these types of suspension bridges is a walkway formed by, or supported by, hanging vines and vegetation.

These different approaches are determined by a variety of circumstances but all are responses – in various and appropriate ways – to the four basic types of forces that act on bridges, either singly or in combination: tension, or a tendency to stretch or pull apart; compression which pushes together and compacts; shear, which is a sliding force; and torsion which is a twisting force.¹¹ The form of the bridge, and the materials used in its construction, also create different – and utilize different – structural forces.

A bow-string truss or tied-arch bridge: the horizontal thrust of the arch, from which the carriageway or deck is supported from above, is restrained by the horizontal tie on which the carriageway sits.

For example, the beam in a beam bridge is under both compressive and tensile forces, itself exerting a downward, compressive force on its piers. The weight of arched bridges is carried downwards from the crown to the ends of the arch and then not only vertically but also laterally because an arch, by its nature, thrusts outwards. The force of an arch’s lateral thrust depends largely on its form, but also to a degree on its materials of construction and sheer mass and weight. Clearly, a shallow, elliptical arch of masonry will have more lateral thrust than a semi-circular arch formed with timber members. For the arch to function structurally this outward thrust must be contained – possibly by a horizontal tie linking both ends of the arch but usually, in bridges, by abutments that exert a compressive force to prevent the arch from spreading apart.

In addition, the material from which a masonry arched bridge is constructed is under compression, being forced together by the loads carried and by gravity. This is why an arch made of brick or stone voussoirs is such a perfect form for a load-carrying structure – the more weight that is placed upon it (within reason) the more rigid it becomes because the load ensures that the components are locked more firmly together.

A suspension bridge, in which the carriageway is supported almost fully from above: the suspension cable, passing over the tops of the suspension towers and anchored firmly in the ground, is connected to the carriageway by vertical suspender cables.

The Forth Railway Bridge, Scotland, completed in 1890: balanced cantilever arms linked by suspended spans.

In contrast, bridges with their carriageways suspended from cables are structures operating under tension because the loads on the carriageway pull – or stretch – the cables.

These basic strategies can be combined to create composite structures in which different members are acting under both compression and tension. For example, the cantilever bridge is a more complex version of the beam bridge, utilizing additional structural principles. The Forth Railway Bridge of the 1880s in Scotland is a useful illustration (see page 294). It incorporates massive steel lattice-work pylon towers, forming projecting ‘arms’ that are, in effect, huge balanced cantilevers linked by suspended spans.

The loads at work within the lattice towers of the Forth Bridge are complex, with vertical members in compression and diagonal members in tension, but broadly speaking, the upper raking steel principle members of the cantilevers are under tension, being pulled down by the weight of the carriageway below them, while the lower steels of the cantilevers are under compression, being pushed down by the weight of the carriageway above them. The structure of the Forth Bridge confirms an ancient and elegant engineering ideal expressed in such great Gothic cathedrals as Notre Dame in Paris or Reims. In this ideal engineering model, conflicting forces are made to balance, to compensate for each other, with thrust met by an opposite and equal counter thrust, and weight balanced by weight, all calculated to create structural equilibrium and to achieve strength and solidity not through mass but through pure engineering know-how.

Another fascinating example of a bridge design embracing and utilizing different structural forces is the bow-string truss bridge, or tied-arch bridge, in which the outward, horizontal force of the arch is restrained by a horizontal tie rather than by abutments and the bridge’s foundations. Ideally the horizontal tie – when linked to the arch by vertical and diagonal members – also functions as the carriageways – as in the great examples of the type bridging Sydney Harbour and the River Tyne in Newcastle (see pages 219 and 179).

The design of this type of truss – which by necessity must be made of metal or timber – was perfected in the second half of the nineteenth century by engineers who were fully able to calculate forces at work in bridge construction and in the natures of different materials. These engineers were obliged to do so because of the unprecedented methods of modern transport in which increasingly heavy and rattling railway engines and their carriages put particularly strong stresses on bridges. One of the pioneers of the precisely calculated and very strong metal railway bridge, was the American engineer Squire Whipple, who in 1841 patented his all-iron bow-string truss bridge design. In Whipple’s conception, a pair of these arched trusses, set side by side, carry a carriageway set on a platform built off the beams forming the strings. But the key point about Whipple’s bridges was not so much their form but the fact that all was calculated by scientific analysis and the size of all members dictated by the forces they carried. His book, A Work on Bridge Building of 1847, is one of the key nineteenth century publications on structural mechanics.

The choice of form chosen for the bridge usually depends on a number of factors: on the width, height and type of obstacle to be bridged; on the function of the bridge and estimated forces of ‘dead’ and ‘live’ loads; on time and materials available for use (masonry and cast-iron were really only appropriate for compression structures while more flexible or ‘elastic’ timber, wrought-iron or steel worked for tensile structures); and – of course – on the skill, knowledge, intentions and nerve of the bridge builder.

BRIDGE OVERVIEW

The principles of bridge construction, and the problems and potential of different forms and materials, are best explained in further detail by reference to a few specific examples of bridges. For reasons of clarity and instructive comparison, the examples are arranged and grouped according to primary construction materials.

Timber

Timber is, presumably, the earliest bridge-building material in large scale and continuous use. Only when grandeur or longevity was required, or in regions with no easily available timber – such as Mesopotamia – would stone or brick have been used in preference. And when timber is used the beam-type design, incorporating piers, is the obvious choice if reasonably short unsupported spans are acceptable. Two early timber bridges survive and are available for scrutiny – not in physical reality but in informative contemporary descriptions. During the Gallic War, in 55 to 53 BC, Julius Caesar built two military bridges over the River Rhine. The purpose of the bridges was both strategic and political. They were to demonstrate to aggressive tribes east of the Rhine that Roman power was ubiquitous, that the legions could roam at will – even the mighty Rhine was no obstacle – and that they didn’t need to scrabble around in boats, but could move with majesty and dignity over the water.¹²

The first bridge was located between Andernach and Neuwied, and took 40,000 legionaries ten days to build. It was 140–400 metres long and 7–9 metres wide, across 9 metres of water. Caesar’s description of the bridge’s construction is obscure and has led to disputes about its exact design. But it is clear that the carriageway rested on piles, each formed by a pair of pointed logs 0.46 metres (1.5 feet) thick and fastened together 0.61 metres (2 feet) apart. The two-pronged piles were driven into the riverbed using pile-drivers, ‘not vertically…but obliquely’, set alternately so as to be ‘inclined in the direction of the current’ and ‘in the opposite direction to the current’. Such was the ingenuity of the design that ‘the pairs of piles…each…individually strengthened by a diagonal tie between the two piles’ formed a ‘structure…so rigid that in accordance with the laws of physics, the greater the force of the current, the more tightly were the piles held in position’.¹³ This description suggests that trusses were created to stiffen the bridge. After the bridge was used for punitive raids and to demonstrate the power of Rome, it was completely destroyed so that it could not be used by attacking forces. Clearly Caesar was not convinced that his threats had entirely worked on the warlike tribes of Germania.

The second bridge was constructed in a similar manner and for similar reasons at Umitz and then partly dismantled. At about the same time, Vitruvius was writing his Ten Books of Architecture. Although his text touches on most aspects of building he says virtually nothing about bridges. That such an important civic and military work should be omitted is very strange, and suggests that Vitruvius’s work was either incomplete or that parts are now missing. In contrast, Leonardo da Vinci tried his hand at the design of timber bridges, perhaps inspired by Roman precedent, with one surviving sketch of 1490 showing a complex trussed construction incorporating a two-tier passageway.¹⁴

In 1513 Fra Giovanni Giocondo published a scholarly rendering of Caesar’s bridge in his edition of Caesar’s Commentaries. Andrea Palladio, always keen to try his hand at the analysis and reconstruction of ancient buildings, included in his Quattro Libri of 1570 a very accurate interpretation of Caesar’s account (Chapter IV, Book Three).

Palladio also, in his Quattro Libri, included an illustration (Plate VI, Book Three) of a bridge just completed to his own designs – at Bassano del Grappa in north Italy – that must in part have been influenced by Caesar’s description of the Rhine bridges. Palladio’s bridge is a most curious affair that crosses the River Brenta by means of timber beams supported on timber piles formed by logs set obliquely – somewhat as described by Caesar – to counter the current of the river. The bridge, roofed to protect both its passengers and its timbers from the weather, survived until 1748. It was then rebuilt but again destroyed – this time during the Second World War – and has since been faithfully rebuilt to Palladio’s original 1569 design.

A perhaps more remarkable design in the Quattro Libri – remarkable, that is, because of its pure utility – shows a series of variations for the construction of a bridge over the 35-metre-wide Cismone River (Plates III to V, Book Three). All the variations show trussed or triangulated timber structures – some slightly arched, others with flat carriageways – with individual timber members joined with wrought-iron straps and pins.¹⁵

Timber-built bridges became something of a speciality in those regions where wide rivers or gorges abounded and where timber, rather than stone or brick-clay, was in ready supply as a building material. Timber was the dominant construction material in much of the Himalaya region – for example, the roofed cantilever bridges of Bhutan and Tibet and in Japan, where a sensational and very beautiful example is the Kintaikyo Bridge at Iwakuni. Here five steeply rising timber-built arches – with timbers wedged and dove-tailed together – leap from stone piers, like a great serpent. The bridge was built in 1673 but the timber arches have been regularly rebuilt (originally without nails) in the traditional manner.

The Kintaikyo Bridge, Iwakuni, Japan, was first built in 1673. The centre three timber spans – each a 35 metre width – has been rebuilt every 20 years and narrower outer spans every 40 years – initially without nails. All fully rebuilt in the early 1950s after wartime neglect.

The Blenheim Covered Bridge, New York State, USA. Built between 1855 and 1857, it incorporates a clear span of 64 metres.

Eighteenth-century Switzerland was also a place in which timber bridges became something of a speciality. Here the brothers Johannes and Ulrich Grubenmann, both skilled carpenters, constructed a series of timber bridges of pioneering form and large scale. Most have been long destroyed, such as the one of 1757 at Reichenau that had a span of 67 metres, but their Rümlang Bridge at Oberglatt survives. Built in 1766, it spans 27.5 metres by means of struts, trusses and arches. To help protect the structural timbers from the weather, the carriageway is roofed.

Carpentry was also the solution when a bridge was required in many regions of North America during the first half of the nineteenth century and before the ready availability of cheap iron. Some of these American structures were of huge size and, through engineering ingenuity, achieved surprisingly long spans. For example, the bridge of 1812 across the Schuylkill River, just outside Philadelphia, had a clear span of 103.56 metres and so earned itself the name Colossus. The designer, Louis Wernwag, was in part able to achieve such a wide span by incorporating iron rods with the timber beams. In 1838 the bridge suffered the fate feared by all builders of wooden bridges: it caught fire and was utterly destroyed. The other thing greatly feared by the builders of timber bridges – especially those constructed with softwood – was rapid decay. Softwood can only survive the elements if regularly painted, a hard or very expensive thing to do with bridges, so American bridge builders tended to take up the other option – a shingle-clad roof over, and wooden walls around, the structural timbers and trusses.

The Colossus wasn’t roofed, but a timber bridge built across the Schuylkill River a few years before had been. The Permanent Bridge in Philadelphia, designed by Timothy Palmer and opened in 1805, is regarded as the first covered bridge built in North America.¹⁶ Covered bridges built of softwood, if properly detailed, with roof cladding maintained, and if fortunate enough to escape fire, can protect themselves from the weather and prove incredibly long lasting. The Permanent Bridge lasted until 1850. The oldest covered timber bridge surviving in the USA today is located at Hyde Hall, East Springfield, New York State, and dates from 1825.

As early as the 1840s, large-scale, covered bridges had become internationally recognised as something of a North American peculiarity. Charles Dickens, when travelling through the land in 1842, went to explore one crossing the Susquehanna River in Pennsylvania, and described it as ‘nearly a mile in length…profoundly dark…interminable…with great beams crossing and recrossing it at every possible angle’. He admitted to being ‘perplexed’ and, due to the gloom and the echo of the ‘hollow noises’, like being ‘in a painful dream’.¹⁷ The bridge was indeed nearly a mile long, its carriageway supported on piers, and it was burned and destroyed during the Civil War.

The timber- built truss structure of a mid-nineteenth century North American covered bridge. Its soft wood structural timbers are protected from the weather by timber boarding.

Blenheim Bridge, Schoharie Valley, New York State, built between 1855 and 1857, is a very fine surviving and early example of a timber-built covered bridge. It has a total length of 70.7 metres that incorporates a clear span of 64 metres – the longest single span of any wooden covered bridge in the world. The bridge is built of pine with its length formed by three trusses, with huge pine posts, braces and counter-braces, which are based on a prototype designed in 1830 by Stephen H Long, known as the ‘long truss’, and once much-emulated. The centre truss rises higher than the other two, and within it is enclosed a pair of arches – wrought of oak – rising from the lower ‘cord’ or carriageway up to the level of the roof ridge. The engineer-cum-carpenter of the Blenheim Bridge, a masterpiece of big-boned, heavy-duty timber construction, was Nicolas Powers from Vermont.

The Bridgeport Covered Bridge of 1862 over the South fork of the Yuba River near Grass Valley, California, incorporates a clear-span almost as long as that of the Blenheim Bridge – 63 metres. The Bridgeport Bridge includes two parallel trusses based on a design that was patented in 1840 by William Howe, a Massachusetts millwright. Howe trusses are designed so that – unusually – diagonal members are in compression and vertical members in tension. The designer of the bridge, David Ingefield Wood, was seemingly unsure about the ability of the Howe trusses to bridge the wide span or to carry expected loads, so he beefed them up with wide and shallow timber arches. These arches are based on the Burr arch truss – a type designed by Theodore Burr in 1804 and patented in 1817 – which consists of timbers bolted together, squeezing between them the members of the truss. The arches, essentially an auxiliary and independent structural system, rise from huge granite blocks placed slightly below each end of the bridge to just below the eaves of its roof. These arches are expressed externally and give the bridge a powerfully engineered appearance. Other examples of the Howe truss survive in the Jay Bridge of 1857, in Jay, Essex County, New York, and in the 22-metre-long Sandy Creek Covered Bridge of 1872, in Jefferson County, Missouri.

A covered bridge constructed using Burr Arch trusses. The system, incorporating a wide-span timber arch to unite and bolster the trusses, was patented in 1817 by Theodore Burr.

The essential principle underpinning the Burr arch truss design was that the arch should carry the entire load of the bridge while the trusses, of king-post form, should keep the bridge rigid. Good examples of Burr arch truss bridges are found mostly in India and Pennsylvania, such as the Baumgardener’s Covered Bridge of 1860 with a 32-metre span, in Lancaster County, Pennsylvania. But fine early examples survive also in West Virginia – notably those at Philippi of 1852 and at Barrackville, of 1853, both designed by Lemuel Chenoweth. The longest automobile-carrying covered bridge in the US is the splendid 140-metre-long Cornish-Windsor Bridge, of 1866 in Cornish, New Hampshire incorporating a clear span of 62m.

Trestle viaducts

Characteristic in parts of North America was the practice of carrying railway tracks on often highly-elevated and prodigiously long timber-built trestle viaducts. Such things had been built in Europe during the early years of the railway age when speed and economy were required – indeed Isambard Kingdom Brunel was quite a master of the art, constructing over forty in Cornwall alone during the 1850s – but there was nothing to compare with the huge scale of the American creations. Trestle viaducts must have been, in the early years in the United States, truly astonishing and unprecedented things to behold – they must have convinced the innocent and those uninitiated into the wonders of the railway age, that smoke-belching and bellowing steam engines and such monstrous creations as the viaducts were all just part of the Devil’s ride from hell. Studying early photographs of trestles – for many of the best are now long gone – it is still possible to capture some of the original drama of their first appearance.

Unlike traditional buildings, their close-packed structure gives them no obvious grace, and they often look impossibly bizarre or outlandish as they cross ravines or gorges that had lain pristine for eons and impassable to man. They possess instead a sort of crude, utilitarian strength and power that is almost sinister, as if they are bridges built for brute creation. For these reasons, the mightiest trestles are mesmerising to behold, awe-inspiring and tremendous examples of the emotions Edmund Burke explored in the mid eighteenth century in his Philosophical Enquiry into the Origins of our Idea of the Sublime and Beautiful: ‘The emotion caused by the great and the sublime…[the] terrible with regard to sight… is Astonishment…that state of the soul, in which all motions are suspended, with some degree of horror…’.¹⁸ Good examples are the Portage Viaduct, one of the ‘wonders of the age’ when completed in 1852; the vastly long Lucin Cut-off Viaduct across the Great Salt Lake in Utah, built with Douglas fir from 1902 to 1904, disused since the 1950s and now being dismantled; and the long-demolished Bloedel Donovan’s Viaduct of 1920 over the Skykomish River, in King County, Washington.

Of course, long before the end of the nineteenth century, metal started to replace wood for viaduct construction, which resulted in a great reduction in structural bulk and increase in elegance. The Garabit Viaduct in France of 1884, is a supreme example (see page 264), but also memorable are the 625-metre-long and 92-metre-high Kinzus Viaduct of 1882 in McKean County, Pennsylvania, which was grievously damaged by a tornado in 2003; the Meldon Viaduct, Okehampton, Devon, England, built between 1871 and 1874; and the Lethbridge Viaduct, in Alberta, Canada, of 1909, which is the longest metal-built viaduct in the world.

Masonry

Pioneering brick-built bridges with carriageways supported on vaults were constructed in Mesopotamia from at least the sixth century BC – for example, the famed bridge across the Euphrates in Babylon. Stone vaulted and arched bridges, as well as stone lintel bridges are recorded in the Anatolia and Aegean regions from the second century BC. Possibly far older masonry bridges survive in the Peloponnese, Greece, where there are a number of what appear to be Mycenaean bridges dating from around 1,300 to 1,190 BC. A good example is the 22-metre-long Arkadiko or Kazarma Bridge, near Tiryns, that is constructed with cyclopean masonry in typical Mycenaean manner and incorporates a corbel arch. However, the earliest surviving masonry bridges, with verified histories and that represent a coherent body of work, are those built by Rome (see pp 56). A good, typical and early example is the Ponte Fabricio, in Rome of 62 BC and restored AD 19 that crosses the Tiber to an island by means of two semi-circular arches, separated by a narrow higher arch to allow floodwater to pass without putting undue lateral pressure on the bridge. Other examples include the Ponte Milvio in Rome, of 115–109 BC, that carries the Via Flaminia into Rome on five wide semi-circular arches, and the Ponte d’Augusto, of AD 50, in Rimini. A fascinating Roman period bridge is the Romi or Sasani Bridge at Dezful, Khuzestan, Iran. It was constructed in AD 250 by Shapur I, ruler of the Second Persian Empire, who may have used Roman engineers captured when he defeated Emperor Valerian.

Although Roman structural theory – and aesthetics – preferred the use of arches of semi-circular form, the advantages of segmental arches were recognized (with the possibility of greater span they could bridge a river with fewer piers) and occasionally applied. For example, the now ruined Limyra Bridge, at Lycia in Turkey, that incorporates wide-span segmental arches – some up to 15 metres in span – to create a bridge with a very low height; the Alconétar Bridge across the Tagus, in the Extremadura region in Spain, built perhaps during Emperor Trajan’s reign by Apollodorus of Damascus and now in ruins; and the also ruined Ponte San Lorenzo, Padua, of 47 BC, with very slender piers and spans of up to 14.4 metres. The sorry states of most of the Roman bridges incorporating segmental arches would suggest that this form was not particularly stable and certainly not able to take the buffets of time as well as the more robust semi-circular arched bridges.

A particularly intriguing early stone-built bridge is the Malabadi Bridge over the Batman River, Diyarbakir, Turkey. It was built around 1146 during the Seljuk period, has booths or hostels at either end, and rooms for travellers – indeed a caravanserai – located within its spandrels. Its main, central, arch is slightly pointed and has a span of 38.8 metres – at the time one of the longest in the world.

Of similar date, but very different in form, are the corbel arched bridges of Cambodia, such as the twelfth to thirteenth century Naga Bridge, at Angkor Thom, on which gods and demons pull on a huge snake, stirring the ocean of milk as in the Hindu creation myth. The longest of the type – stretching 75 metres, is the Kampong Kdie Bridge in Cambodia dating from the twelfth century. The corbelled-out construction of the arches allowed only very limited spans but, in consequence, created no hump or rise in profile so such bridges made excellent flat and even causeways, leading across lakes to temples, and fine places for the display of sacred art.

The Malabadi Bridge, Diyarbakir, Turkey, was constructed around 1146 and its masonry-built and slightly pointed arch has a span of 38.8 metres - at the time one of the longest in the world. Rest rooms for travellers, a caravanserai, - are located within the bridge’s haunches.

In western culture, immensity of scale – particularly of span – grew increasingly important as the practical demands of bridge construction increased. This culminated with the brick-built Maidenhead Bridge in Berkshire, England, designed by Isambard Kingdom Brunel for the Great Western Railway and completed in 1839. It incorporates a pair of shallow segmental aches, each with a span of 39 metres, making them the longest and flattest brick-built arches ever formed. In 1902 the Rockville Bridge over the Susquehanna River was completed in Harrisburg, Pennsylvania and which – with a length of 1,150 metres, became – and remains – the longest stone-arched bridge in the world. This bridge – offering a vast, open and noble promenade across the river – would surely have delighted Charles Dickens as much as its now long-lost and ‘profoundly dark’ precursor across the river ‘perplexed’ him.

Metal

The age of all-metal bridge construction starts, to all intents and purposes, in England with the epoch-making Iron Bridge, in Coalbrookdale, Shropshire. Completed in 1779, it was the boisterous and precocious child of the Industrial Revolution. It was not the first bridge to use iron, nor was its design revolutionary – indeed its basic form is that of a masonry bridge and its cast-iron members are disposed much as in contemporary timber bridges. But it was the world’s first all-iron bridge, it was the product of new technology – steam power and the efficient manufacture of strong cast-iron components – and it would usher in a new world of bridge construction.

The bridge was designed by Thomas Farnolls Pritchard with ironmaster Abraham Derby III and is, in many wonderful ways, a bridge between worlds. It marks the coming of the new industrial age of mass-production, yet it still possesses a Georgian elegance and regard for ornament. It is made of iron, yet its iron components are mortised, wedged and screwed together as if made of timber. It is a work very much of transition: Derby knew that it was essential for this new material to be used in compression – which is cast-iron’s strength – not in tension, which is its weakness (see page 182). So the bridge is designed to ensure that, as far as possible, loads are transmitted vertically down and individual components are in compression.

The possibilities offered by this newly available construction material were soon appreciated by avant-garde architects and engineers such as Thomas Telford, who in 1795 specified cast-iron to form the troughs of the vast Pontcysyllte canal aqueduct across the Dee Valley outside Llangollen, North Wales. The troughs, made with cast-iron slabs dovetailed together – like keystones in an arch of lintel – for greater compressive strength, sits on 35-metre-high, stone-built piers, each 16 metres apart. These are of slender, tapering form and of ingenious honeycomb construction (with stone laid in mortar containing ox blood as a hardener) to reduce weight and materials used. Within the cast-iron troughs water rises almost to their brims, and a railing and towpath are placed only on one side so that barges float high above the valley, enjoying unrestricted views, as if navigating through the clouds. The aqueduct was opened in November 1805 and is one of the most beautiful, robust and continuingly useful creations of Britain’s early Industrial Revolution.

Key characteristics of cast-iron were that components made in the material were not only strong – which meant they could be slender in section and still possess greater strength than equivalent timber components – but also quick and cheap to produce. These characteristics ensured that the model offered by the Iron Bridge at Coalbrookdale was soon emulated. They also made it possible to develop a new commerce in export architecture, transporting British-forged buildings and bridges – reduced to flat-packs for ease of travel – to all corners of the growing empire.

One of the first and most significant developments of the Iron Bridge was the stupendous Sunderland Bridge across the River Wear in County Durham. It was started in 1793, completed in 1796, rose to a height of nearly 30 metres above the surface of the water (which had involved the design and erection of a superbly designed system of timber scaffolding), and had a span of 72 metres. Its promoters and designers were Rowland Burdon and Thomas Wilson. The huge arched bridge, made in an elegant manner out of pioneering material, was regarded as one of the technological glories of the age. But, sadly, glory proved only transitory, and due to gradual deterioration all was demolished in 1929. But the great bridge left more than a trace behind. Such was its fame, that copies were eagerly desired around the world and – thanks to the character of cast-iron that favoured pre-fabrication – this desire could be fairly easily fulfilled with components cast to the required scale and then shipped abroad for assembly on site. And so, in 1800, crates of cast-iron arrived in Spanish Town, Jamaica which by 1810 – after the construction of substantial stone abutments – had been bolted together to form a reduced-scale version of the Sunderland Bridge. Known as the Rio Cobre Bridge, it is now the oldest iron bridge in the western hemisphere.

If the Rio Cobre Bridge is one of the most curious of iron bridges, then Isambard Kingdom Brunel’s bridge masterpiece – the Royal Albert Bridge, Saltash, Cornwall – is one of the most stunning. The last great work of Brunel’s career was completed in 1859, and all ornament and all reference to history has been dispensed with: it is a masterpiece in pure, raw, and beautiful function.

Vast trusses of ‘lenticular’ form span 139 metres between piers, the centre founded in a small rocky island, and rise 24 metres above high-water mark. The lenticular trusses incorporate massive tubular arches made from wrought-iron that rise above the track, with their ends tied with chains forming inverted arches. The object of this design was to prevent the trusses transmitting any outward horizontal thrust. It is fascinating to compare the construction of the Saltash Bridge with the near contemporary works of Robert Stephenson, such as the High Level Bridge in Newcastle-upon-Tyne, with which Brunel was very familiar (see page 213). The trusses on Stephenson’s slightly earlier High Level Bridge in Newcastle-upon-Tyne (see page 190), perform in much the same manner as Brunel’s ‘lenticular’ trusses and must, to a degree, have been an inspiration.

One of the particular problems Brunel encountered at Saltash was the digging of the foundations for the piers that rise from the riverbed. The solution he chose – ‘pneumatic caissons’ – was a very modern one that had not been tried and tested. The system had been used first by John Wright in 1851 for setting the foundations for piers for the bridge across the River Medway at Rochester. Pneumatic caissons were an intriguing and seemingly very sensible idea that utilized the potential of modern technology. Airtight caissons – essentially vast drums open at top and bottom – are wrought, towed into position, sunk so that their bottom edges sink into, and are sealed by, soft mud or sand. Then the tops, standing well above high water mark, are sealed, and compressed air pumped in to keep water and mud from entering. To retain air pressure inside the caisson, workmen were to enter and exit the sealed chamber by means of an airlock.

A lenticular truss of the type used by Isambard Kingdom Brunel for his Royal Albert Bridge, Saltash, England, completed in 1859. The large wrought-iron tube forming the top arch of the truss is tied, or restrained, by the lower, inverted, arch made of a chain fabricated of wrought-iron bars. This design means that the arched truss exerts no outward thrust.

There was even a system devised for removing material – ‘muck’ as it was called – to the surface by means of a pit, filled with water to act as an airlock, via a ‘muck tube’ that was cleared by a crane fitted with a clamshell bucket. The water-filled ‘muck tube’ also helped to regulate pressure in the working chamber. Excess air pressure could escape through it and the tube could be used to prevent water pressure dropping – which was essential if water and mud were to be prevented from flowing into the caisson.

It was all very ingenious – the only problem was that the system killed or crippled people. The engineers didn’t know anything about what happens to the human body when it toils within a compressed atmosphere, and they had no concept that bubbles of gas can build up in the blood, and expand when a normal – decompressed – atmosphere is re-entered too quickly, causing not only great pain but serious, possibly terminal, physical damage. This distressing condition is also suffered by divers who ascend rapidly after spending too long a time at a great depth and has become known as ‘the bends’.

Although this mysterious ailment was quickly associated with pneumatic caissons, indeed it became known as ‘caisson disease’, ambitious engineers did not abandon the use of this useful time-saving invention and in 1872 it even caused the disablement of the engineer Washington Roebling when supervising the construction of New York’s Brooklyn Bridge (see page 287). When James Eads started construction of his epic railway bridge across the Mississippi at St Louis in 1867, he was under intense time pressure with loans only becoming available when specific construction targets had been achieved. So, naturally pneumatic caissons were the preferred option which, with men working up to 28 metres below water level, resulted in the deaths of fifteen men, the crippling of two, and serious injury to a further seventy-seven.

Due in part to these woeful sacrifices, Eads completed construction on time, and as it happens created one of the most significant bridges ever built. It crossed the river in three mighty arches, the longest with a span of 158 metres, and all constructed out of steel – which was the first time this material had been used so extensively in any major building. It was also the first time that a cantilever support system was used to aid bridge construction, with the arches being built outward from the piers, secured by guy wires, and used as platforms from which to continue construction until the two halves of the arch met.¹⁹ This method reduced the need for expensive scaffolding but, more important, was – to all practical intents and purposes – the only way to build a large bridge across the wide, deep and fast-flowing Mississippi.

The opening of the bridge on 4 July 1874 was a gala event. The poet Walt Whitman was present and soon declared the bridge ‘perfection and beauty unsurpassable’. A few days later, having had the aesthetics of his bridge so pleasingly praised, Eads demonstrated the solidity of the bridge to a wondering public by leading an elephant over its spans and then, realising this was perhaps not quite convincing enough, sent fourteen locomotives across the bridge, one after the other. The bridge (now known as Eads Bridge) was indeed a modern wonder. Popularly regarded as beautiful, evidently strong, and a record-breaker because its length of 1,964 metres made it the longest arch bridge in the world. Eads’ bridge was in many significant ways a model for, and portent of, things to come.

The Eads Railway Bridge across the Mississippi at St Louis. Started in 1867 to the designs of James Eads, the bridge pioneered the large-scale use of steel in construction and when completed in 1874 was the longest arch bridge in the world.