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CHAPTER ONE

EMPIRE

The Pont du Gard, near Nimes, France: an aqueduct built around 2,000 years ago and one of the greatest surviving monuments from the Roman world. The stone blocks projecting from the pier serves as supports for timber scaffolding and centering during construction and maintenance.

ROME, MORE THAN ANY EARTHLY POWER BEFORE or since, expressed its might and its aspirations through architecture and engineering. It took the architecture of the past – of the Egyptians, the Greeks and the Etruscans – and transformed it to suit its own needs and to realize the demands of its growing empire. New functions such as roadways and water supplies emerged, demanding new types of buildings, and these could only be achieved through a radically evolved understanding of the potential of engineering. A series of spectacular developments took place, notably the rapid refinement of structural systems incorporating round-headed arches and domes, giving rise to buildings of unprecedented scale and complexity in which new materials such as concrete (see page 312) were used in major roles for the first time. Roman bridges are a perfect illustration of how awe-inspiring beauty can emerge from innovative engineering.

Rome’s breathtaking and groundbreaking contribution to the development of architecture was characterized by an ever-growing appreciation of the potential of engineered structures in which the forces of nature were harnessed and tamed to complete projects that would have been beyond even the imagination, let alone the practical grasp, of earlier generations. The resulting structures combined the cardinal architectural virtues identified by the Roman architect Vitruvius over 2,000 years ago – ‘commodity, firmness and delight’ – by which he meant an architecture that simultaneously fulfils its functional requirements and is stable, while also being poetic and imbued with a power to inflame and engage the intellect.

The aqueduct in Segovia, Spain, constructed during the 1st century AD, snakes through the town, its conduit supported on increasingly tall tiers of arches as the ground level falls away.

Roman architecture, at its best combining sublime beauty with function, often played a vital role in consolidating and spreading Roman power and maintaining its civilization. This fascinating combination of characteristics is perhaps best expressed by the bridges and aqueducts that Rome created throughout its empire. Their roles as routes of communication and the means of supply were of vital importance to the well-being of the Roman world. Aqueducts brought a plentiful supply of water – essential for the Roman concept of civilized life – and roads transported goods and luxuries over great distances, allowed wealth creation through trade, and security through speedy troop movements. In addition to being functional objects, bridges and aqueducts were also intended, in their design and solidity, to express Rome’s cultural aspirations and the longevity of its vision. Together, these intentions produced structures of intense beauty – a beauty that comes from the pure and powerful realization of functional demands and of the way in which the potential of available building material can be enhanced through design.

A remarkably large number of Roman bridges survive, in whole or in part, still fulfilling their original function within the former empire. They continue to astonish, inspire and delight, through their scale, fitness for purpose and often daunting engineering boldness. But there are four Roman bridges that haunt my imagination. They epitomize Roman engineering genius, in which sublime and utterly moving beauty is achieved by the almost ruthless observance of function. They are the essence of engineering, and also the essence of architecture at its best. There is little about their design and construction that is superfluous to function or to pertinent meaning. Their stones carry messages, about the power of engineered structure and about the seemingly eternal power of Rome. In all these bridges each detail possesses an intensity of meaning and beauty: even those that appear ornamental are in fact calculated to add extra cultural or spiritual significance, raising purely utilitarian design into the poetic realm of architecture.

All of these structures lie outside of Italy. Two of them, the Pont du Gard in southern France near Nîmes and the aqueduct of Segovia in Spain, carried the very life-blood of Roman civilization: abundant water. The others, the Alcántara Bridge over the River Tagus in Spain, and the Pont Flavien, in Saint-Chamas, Bouches-du-Rhône, France, seem to have served a largely military, strategic and triumphal purpose marking the omnipotent presence and power of Rome. But each one, in its solidity and scale, seems to have been built in defiance of nature. And yet this is not quite so, for it is the essential paradox of engineering that the violence of the forces of nature can only be withstood by man-made structures that fully utilize the forces of nature. The fact that these structures survive after 2,000 years or so – with all significant damage being the work of man and not natural forces – demonstrates most succinctly how well these Roman engineers understood their work.

The Pont du Gard is a stupendous aqueduct located about 29 kilometres north of Nîmes. As its name suggests, it spans a valley through which the river Gard winds. It forms part of a conduit constructed to carry the waters of the Alzon some 50 kilometres to Nîmes and, rather appealingly, no one is absolutely sure of its date. The current consensus of opinion is that the aqueduct was started by Marcus Vipsanius Agrippa, the brother-in-law of Emperor Augustus in about 18 BC and that the Pont du Gard itself is around 2,000 years old, although some argue that it dates from the mid first century AD. But what is more certain is that the Pont du Gard is one of the most moving and awe-inspiring structures to survive from the ancient world. The first glimpse you get of it is a virtual assault on the senses: its scale is majestic, its form intensely pleasing and it soon becomes clear that most of the architectural details that it sports are not merely ornamental but are expressions of the means of construction.

An intimate view of Roman precision engineering: a vista along the conduit on top of the Pont du Gard. This is the only place in the structure where mortar was used – necessary to ensure water did not leak through the joints in the masonry.

The aqueduct has an overall length of about 262 metres and comprises three distinct tiers of structure. The lower tier is formed by six wide arches (each spanning a distance of something between 15.2 and 24.3 metres) which support a roadway. From this roadway rise arches similar in size to, and with their piers set over, those below. But this second tier is made up of 11 arches because the cliff faces forming the river valley taper dramatically as they rise higher. On top of the second tier sits the prime purpose for this astonishing structure: a stone-roofed conduit that carries the water to Nîmes. This conduit is supported on narrow-span round-headed arches – three to each wide arch on which they sit – of which thirty-five still survive. The rhythm and elegance of these arches is immediately striking. It was usual in Roman arched structures of this type for the piers to be one third the width of the span of the arch, a width that led to strong piers that could, if one arch collapsed, act as abutments to prevent the whole structure collapsing like a row of dominoes. But here the piers are spectacularly slender, just one fifth of the arch width. Clearly the men who designed and built the Pont du Gard had great confidence in their abilities, and in their creation. And they were right, through their daring they made not only a thing of strength but also of intense beauty. The Pont is incredibly pleasing to look at, its arches reading up from the water, one to one to three, are like a harmonic ratio. The pattern of arches gives an immensely satisfying appearance and feeling of strength, of an object built for eternity.

The vast lower arches, one upon the other, carry a more delicate structure and it’s this delicate upper structure that is the business-end of this engineered marvel. Nothing here is for show: everything is designed and built to support the relatively small conduit running 48.7 metres above the river, constructed with a slight fall so that the water within it could flow serenely from Uzes to Nîmes.

This is indeed heroic architecture, the epitome of that produced in the ancient world. It’s a thing intended to last and is built on a heroic scale to fulfil a seemingly modest function. Yet it carried one of the blessings of civilization – a ready supply of water – to thousands of people. It made cities habitable, farms verdant and people clean, healthy and happy.

As if the form, scale and proportions of the Pont du Gard are not enough to impress, its materials and techniques of construction are almost as remarkable. From the huge blocks of stone from which it is wrought, there are, here and there and in regular fashion, strange protuberances. These tell of the way the structure was made. The stones were cut at a quarry on the riverbank and carted to the site as massive cubes – some weighing 6 tonnes or more – and then hoisted into position using one of the variety of lifting machines Roman builders had at their disposal. But as with all arched and domed structures, the construction process and maintaining stability are problems.

Arches and domes are immensely strong forms – especially when rendered in solid masonry – for their very shapes become stronger as they bear the downward force of gravity, the ‘dead’ weight of their materials and the ‘live’ weight of any loads they might carry. This is a very direct example of strength through design. But by their very nature, these curved forms, although immensely strong, exert some of their load in a lateral direction. Domes and arches want to spread, and so have to be restrained by adequate abutments or buttresses. On the Pont du Gard this is achieved by the piers, which are ultimately restrained and stabilized by the immovable cliff faces, onto which they pass the weight they carry, giving them stability.

But another problem with arches and domes – especially when being built high and on a large scale – is stability during the construction process, before all the forms are locked in equilibrium and before the final keystone is in place. The favoured way in the Roman building world to achieve stability during construction was to support the incomplete dome or arch on a timber scaffold, shaped and engineered to carry the structure until it was complete and could carry itself. This scaffolding was known as ‘false-work’ or ‘centering’. What’s fascinating about the Pont du Gard is that completed elements of its structure – notably the piers and the springings of the arches – served as part of the system of scaffolding that was used to help support those parts still under construction. So the stones protruding from the face of the piers supported timbers that formed part of a scaffold that allowed masons to work on the higher portions of the Pont. The same is true of the bold cornices at the springing level of the arches and the ribs that project from the ‘intrados’ or lower face of the arch. Both these details were not intended to be primarily ornamental but to provide a firm lodging-place for the timber centering required for the construction of the arches.²⁰ A number of these strange projections could have been removed when construction was complete, but it seems that the engineers here saw no need to remove the evidence of the construction process and, more to the point, everything could be used again, in various ways, for any necessary repair work. So, at one level and among many things, the Pont is a permanent scaffold carrying fixing points for use in its own future maintenance. This is an astonishingly far-sighted and very modern concept.

Equally ingenious as this designed-in system of maintenance, is the way in which the stones used in the bridge were cut and fixed together. The engineers realized that maximum strength would result from maximum precision, for if the individual stones fitted tightly together movement would be minimal. Precision was difficult to ensure, but the masons here achieved it to such an extent that the stones are laid without mortar (except in the conduit at the top), which was a huge bonus in itself, because without mortar to be washed away by rain, or blown by wind, or cracked by frost, there would be no need for regular re-pointing to keep the structure sound. The Roman engineers really were creating buildings to last for eternity. The ambition is incredible and the achievement massive. The world that created this mighty work has long gone, but its vision endures in work as steady and timeless as nature itself.

The scale and quality of the construction that the engineers and masons achieved can only be properly appreciated by considering for a moment the tools and machines at their disposal. They had picks and chisels made from hardened iron for working stone, which were adequate, with skill, application and time, for cutting limestone and sandstone with precision. They also used water power to operate stone saws and lifting machines, though not to any great extent.’²¹ Construction work, from cutting and transporting stones to raising them into place, was a very important part of the economy of the Roman state. It was a way of creating work and jobs, keeping people employed and out of trouble, and of getting money to flow through society. For example, Emperor Vespasian (AD 69-79) refused to let builders use water-driven hoists ‘lest the poor should have no work.’²² So in place of mechanical power, the Romans preferred – almost as a matter of state policy – to achieve lifting largely by muscle power, operating cranes or systems of pulley blocks hung from legs or poles and worked by winch or capstan. Using these devices, heavy stones were lifted by slings, or gripped by pincers or a kind of ‘lewis’, a lifting tool comprising metal bars inserted and wedged into a dovetailed cavity cut in the top of a block of masonry.

Detail of the Pont du Gard showing piers rising from the lower arcade. The projecting stones were supports for timber scaffold during construction.

Metal was also used in construction, usually in the form of wrought-iron cramps or bars set in lead and then placed in cut recesses to bond stones together. As Vitruvius explains when discussing how to avoid the problem of crumbling mortar: ‘…leave a cavity behind the [facing wall]…on the inside build walls two feet thick…and bind them to the fronts by means of iron clamps and lead.’ Work executed in this way, Vitruvius claimed, ‘will be strong enough to last forever.’²³

Vitruvius also had some specific things to say about aqueducts, reminding his readers of the importance of an adequate and reliable water supply and stating that for aqueducts or ‘conduits’ the masonry should be ‘as solid as possible and the bed of the channel have a gradient of not less than a quarter of an inch for every hundred feet, and let the masonry structure be arched over, so that the sun may not strike the water at all.’²⁴ Vitruvius also recommended that, when the water carried in the conduit reaches the city it should be held in a ‘reservoir with a distribution tank in three compartments.’ The system was intended to segregate water used for different purposes and to prevent people tapping into the main flow and stealing public water for private use.²⁵ Vitruvius also recognized that water quality was very important, so recommended that it was best to conduct water through clay pipes rather than lead pipes because ‘water from clay pipes is much more wholesome than that which is conducted through lead pipes, because lead is found to be harmful [and] hurtful to the human system.’²⁶ The evidence for this was the health of ‘plumbers, since in them the natural colour of the body is replaced by a deep pallor’ caused by lead fumes that ‘burn out and take away all the virtues of the blood from their limbs.’²⁷ Vitruvius’ recommendations seem to have been used by the Rome official Sextus Julius Frontinus who in about AD 80 wrote a treatise on the Aqueducts of Rome, in which he described the condition of the city’s water supply, actions needed to prevent water leaks and theft, and, in general, promoted Vitruvian theory.

An interpretation of a stone-lifting pulley block.

A view of a Roman period water supply system, including covered aqueducts. Both engravings date from 1521 and are based on descriptions by the first-century BC Roman architect Vitruvius.

‘The sight of the aqueduct entering the town is among the greatest surviving urban scenes from the ancient world. It was dedicated to Hercules – the legendary founder of the city – and still seems the work of divine heroes.’

Extraordinarily enough, a physical example of Vitruvius’ recommendations and theory survives to this day in Spain. The aqueduct in Segovia was built about 100 or so years after the Pont du Gard, perhaps in about AD 50–100 and, unlike the Pont du Gard, continues to fulfil the function for which it was built. Thanks to the skill and robustness of its construction, generations of maintenance, self-effacing reconstruction, and the soundness of Vitruvius’ thinking, the conduit and aqueduct retains its Roman identity and still carries water 15 kilometres from the Fuente Frio River to the old city of Segovia. Much of this length is at or near ground level, but due to the terrain near the city, 800 metres of the conduit is supported on arches springing from piers up to 28.5 metres high.²⁸ Few things are more moving, in the world of ancient engineering, than to see and hear the water – after nearly 2,000 years – still coursing along its worn but serviceable granite conduit perched high off the gnarled, sun-baked and leaping arches of the aqueduct.

The aqueduct, and the conduit it supports, is an admirable machine for gathering and delivering water to an elevated city, the aqueduct’s height above ground varying to accommodate the terrain and to keep the decline of the conduit as little as possible. When the water arrives in the city it is first collected in a tank known as El Caserón (the Big House) and from there runs along a channel to a tower known as the Casa de Aguas (the water house) where it is allowed to decant and impurities settle. The reasonably pure water then travels nearly 730 metres, at a fall of only one-in-a-hundred, to an outcrop near to which the Roman city was built. Then the aqueduct, rising to its full height of 28.5 metres and comprising two levels of semi-circular headed arches, carries the water into the city, to what is now the Plaza de Díaz Sanz. As with the Pont du Gard, the stone blocks – in this case granite – with which the aqueduct is built are unmortared, their precise construction and weight being enough to keep all standing. Particularly satisfying is the masonry of the voussoirs forming the arches, which are a single block deep. They combine with the horizontal courses of the spandrels to form a perfect example of robust masonry construction, where every block is not just doing its job but is seen to be doing its job in a most reassuring manner. It is possible to ponder these stones for hours without getting in the least bored, wondering at the creation of poetic beauty through purely expressed function.

The sight of the aqueduct entering the town – a seemingly endless arcade of granite with the conduit perched high on the immensely tall and seemingly impossibly slender piers of the lower arcade – is among the greatest surviving urban scenes from the ancient world. It was dedicated to Hercules – the legendary founder of the city – and still seems the work of divine heroes. Goodness knows what the local people felt 2,000 years ago; this mighty work is the power of Rome personified – remorseless and eternal.

The Puente de Alcántara makes a telling contrast with the cyclopean Pont du Gard and Segovia aqueduct so that, together, they encompass the whole spectrum of Roman bridge building. In comparison to the massiveness of the latter two, the Puente de Alcántara possesses a lightness of touch as it springs across the void that it was created to tame. It is, in its daring elegance, the very epitome of engineered architecture.

The Puente de Alcántara is, arguably, the greatest of all Roman bridges. It doesn’t have the widest span (that distinction belongs to the delicate first century BC Pont-Saint-Martin in the Aosta Valley, Italy whose central arch leaps 32 metres) but the Puente de Alcántara possesses an extraordinary harmony in its parts and – as with all great bridges – astonishes in its daring ambition. It is a monument to man’s ability to tackle – and to solve in an elegant manner – the most daunting of structural problems. It rises 52 metres above the bed of the river, its two wide central arches have spans of 28.3 metres and 27.4 metres and its mighty piers – made of granite from a quarry over five miles away and laid without mortar – are each nine metres square, with some of the stones weighing 8 tonnes each.

The triumphal arch in the centre of the Puente de Alcántara, bearing a panel that proclaims the bridge was built in the fifth year of the reign of Emperor Trajan - so in around AD 103.

Like the Pont du Gard, this is indeed a mighty work of man that nature has assailed in vain. All here possesses a sublime and sculptural beauty, there are virtually no classical mouldings used in its design, no details or forms superfluous to function. But the bridge is not simply a structurally supreme but spiritually arid utilitarian structure. It also possesses those details, ornamental and symbolic, that are purely poetic and that transform a great functional work into architecture. And most of these details have to do with the human story of the bridge, and its strategic function in the Roman Empire. At one level the bridge is a monument to the man who made it, and to the Emperor who ordered its construction. In the centre of the bridge is an arch, called by some a ‘fortified gate’ and by others a ‘triumphal arch’. Both definitions are correct because it is both of these things, just as the bridge is both a triumph over nature and a key military installation. The arch made the bridge defensible, or rather made it possible for those who controlled the arch to stop the bridge from being used. Whoever held the arch controlled the road that the bridge gave purpose to. But an inscription on the arch also proclaims – in triumphal manner – that the bridge was built by Emperor Trajan in the fifth year of his reign, dating it to AD 103. The man who actually built the bridge gets a smaller shrine but a far more moving inscription. Opposite one end of the bridge survives a small votive temple, a place in which the god of the river, the valley – of the bridge – would have been venerated. It carries an inscription on a marble slab:

The Puente de Alcántara, Spain, built around AD 103: its dramatic setting demonstrates the heroic and poetic beauty of Roman engineering. On the right hand side is the small votive temple where the god of the river is appeased and where, perhaps, lies buried Caius Julius Lacer, the engineer of the bridge.

‘IMP.NERVAE TRAIANO CAESARI

AVGVSTO GERMAMICO.DACIO.SACRVM PONTEM.

PERPETVI MANSVRVM IN.SAECVLA.MVNDI.

FECIT.DIVINA.NOBILIS.ARTE.LACER.

‘I …. Caius Julius Lacer ….

have built a bridge which will remain forever.’

And remain it has. Indeed the bridge is so elemental a form that it became part of the very landscape and imagination of the succeeding generations that inhabited the region. For centuries after the fall of Rome, the Puente de Alcántara was abandoned – forlorn, desolate, unmaintained – but nonetheless it stood and it was used. When the Moors came to the north of Spain they saw it, they marvelled, and they named it Al Kántarah, literally meaning ‘the bridge’. This is the defining bridge: there can be no rival. But the Moors’ admiration did not stop them breaking one of the smaller arches in 1214 during their fighting with Christian forces, nor did its antiquity and beauty stop French troops demolishing one of the main arches in 1812 when retreating from Wellington’s army. Fortunately, the damage was repaired and the bridge survives – a message from one world to another, a marvellous repository of Roman genius that continues to serve the purpose for which it was designed 1,900 years ago, that continues to glorify the road of which it forms a vital link.

Well-built roads, passable all the year round and virtually impervious to the elements, were almost holy things in the Roman world, routes of trade and cultural growth, of conquest and of defence, the veins of civilization. This high status is reflected by a small and beautiful Roman bridge, dating from the late first century BC, that by good fortune survives in the south of France. The Pont Flavien at Saint-Chamas stands astride the Via Julia Augusta – an important route begun in 13 BC on the orders of Emperor Augustus to link the commercially and strategically important cities of Placentia (now Piacenza) in northern Italy with Arles in southern France. At Arles, the Via Julia Augusta linked with the far older Via Domitia that, dating from the second century BC, was the first Roman road built through Gaul and joined Italy to Spain. Placentia was, of course, linked by road to Rome, so the Pont Flavien – with its single stone arch of modest 12-metre span – formed a small but vital link on one of the key routes from Rome, via Arles and Nîmes in southern France, to Spain. This, plus the fact that the Pont Flavien stood within the zone of the cultural, if not political, frontier between Italy and Gaul, explains its extraordinary and ambitious design. Once seen, this exquisite bridge can never be forgotten.

In its small way, the Pont Flavien is a flawless evocation of Rome, a jewel of a creation, a wonder of preservation that is a window onto a long dead world. To reach the bridge you pass along a narrow and now abandoned stretch of the Via Julia Augusta and the first glimpse you get of the bridge is a pair of stone-built triumphal arches, miniature in scale but big in meaning and magnificence. They guard each end of the bridge and offer an extraordinary perspective to all who approach. The arch in front acts as a proscenium for the one behind: very dramatic and very theatrical, and surely a visual device to let the traveller know they had arrived somewhere very special, that they were now in the frontier zone. This pair of arches, that now look uncannily like the pylons of a nineteenth century suspension bridge, were surely intended to proclaim to all travellers heading west and north that Italy was being left behind, and to those heading south that they were now entering the inner environs of the empire, drawing yet nearer on the imperial highway to Rome itself.

The stretch of road between the arches is short, narrow and now pitted and rutted, scarred by generation upon generation of chariots and carts. But despite being only a stone’s throw in length, this small stretch of road offers a vast leap into the past. To stand on this bridge at dusk is to hover in time. Here, the Rome of 2,000 years ago seems not so very distant a place, the triumphal arches being strange portals that goad the imagination. Each arch is dressed with Corinthian pilasters and carries full entablatures, the friezes of which retain handsome swirls of stone-cut acanthus. This seems celebratory, but at the corners of the arches, set above the pilaster capitals, are carved eagles, surely representing the might of Rome, and above them, carved in the round, are lions drawing back on their hind legs and about to pounce. They seem to offer a fair warning to any traveller to behave or suffer the consequences.

The modest but beautiful 1st century BC Roman bridge at Saint-Chamas, Provence-Alpes-Cote d’Azur region, France. The bridge’s importance as part of the Via Julia Augusta is proclaimed by its pair of small but perfect triumphal arches.

On the bridge is carved an inscription that appears to date from the time of construction.

It refers to Lucius Donnius Flavos, a priest from Rome in the reign of Augustus, who is described as the bridge’s builder. Builder perhaps, designer perhaps, but almost certainly the man who – as a priest – dedicated this work to the gods and called upon them to guard it. The highway was sacred and so too was this bridge: then as a gate to the Roman Empire or to Rome itself, now as an emotive and thought-provoking portal to the Roman past.

Detail of one of the triumphal arches showing the entablature with an eagle and a watchful guardian lion – surely calculated to remind travellers of the power of Rome.