Читать книгу The Road - Hilaire Belloc - Страница 12

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Water Courses. The crossing of water courses does not seem to have been originally in the main a search for a ford. It seems to have been rather a search for good taking-off places upon either side, however deep the water in between. The ford was used, of course, wherever it could be, and in it also the hardness of the passage under water was of even more importance than the depth of water: below, say, 4 feet. But the point to note is that often, and probably in the majority of cases, man in the early times took his short cut across water either by swimming or by taking advantage of floating material, and was much more concerned with the hard bank upon either side than with the depth of the stream.

If you take such a very old road as that of the primitive British trackway whose two branches, from Stonehenge and Winchester, unite in what is called the “Pilgrim’s Way” and make for the Straits of Dover, you find this trackway crossing the Mole, the Wey, and the Medway, as also the Darenth, at places where the obvious consideration has been a dry approach upon either side, and not the local shallowness of the stream. (We must remember in this connection that the word “ford” is used at plenty of places where the stream is too deep for crossing on foot: it means simply “a going.” A false etymology here has misled many historians.) Of more importance to the first makers of the Road than the depth of a water course was its swiftness. We have in this country few examples of swift streams of any magnitude, and none of streams so swift as to be impassable or passable with great difficulty, but where such examples occur abroad it is easy to see what a boundary and obstacle a rapid current afforded. It works in all manner of ways to the disadvantage of travel, it makes both swimming and ferrying more difficult (or impossible), it makes bridging either more difficult or (in early times) impossible, it usually connotes great differences of level, sudden floods, etc., and it also usually connotes changes and variety of currents, as well as the destruction of the banks.

At an early stage in the development of the Road came the use of the bridge, and with the bridge the original chief consideration—a dry approach from either side—was emphasized. It is true that fords were bridged as roads developed, but the bridging of a ford is not the normal origin of the bridge. The normal origin of the bridge, if we judge by any one of the original great roads of Europe, is the replacing of a ferry. Men took the obstacle of a river (on account of its length) as something hardly to be turned, save perhaps in its higher reaches. They made straight for it, seeking only firm ground from which to embark and disembark, and established a boat crossing. To this rather than to the ford the bridge succeeded. They bridged it with increasing success as their material science increased in power, and you may see all over Europe the great bridges thrown, not where the river was shallowest nor where it was easiest to traverse for any other reason, but chiefly where the main road led. In other words, the bridge is a function of the Road rather than the Road of the bridge.

Two outstanding examples of this in Europe are London Bridge, perhaps prehistoric, certainly not much less than two thousand years old, and the bridge at Cologne, to which one might add the bridge at Rouen and the bridges of the Island of Paris, which we know to be more than two thousand years old. But it must be remembered that the bridging of a river, even in primitive times, was the next easiest thing to a ferry, and in some circumstances easier even than a ferry. A bridge need not be built of piles. It may be built of boats, and in principle, even over a broad stream, once you could build a boat bridge at all you could build it of almost indefinite length. What would militate against the effort to make a pile bridge were depth and rapidity of stream, but even these, unless the rapidity were very great indeed, did not prevent the throwing of a bridge of boats.

The bridge as an element in the Road plays a very large part which needs some detailed examination: it develops a whole series of results. The object of a bridge is to give continuity and security to travel across an obstacle of depth: usually an obstacle of running water, sometimes a dry ravine. It is but rarely that a bridge is essential to the mere trajectory of a road. In much the greater number of cases its function can be supplied, though far less perfectly, by a ferry, or a ford, or a graded way down into and up from a depression. What the bridge does is to permit of continued traffic, especially continued wheeled traffic, across such obstacles without delay and without trans-shipment, and at the same time to add, up to a maximum of weight, to security; for it is obviously an instrument more secure than the ferry or the ford, especially for heavy weights.

But the bridge has always represented a special economic effort, greater yard for yard than that of the average of the road of which it was a part; and that is why you almost always find it the mark of civilization. A primitive culture can exist for centuries without bridges. The proportion of bridge-building effort to road-building effort varies very much with the physical science of various times. It is less to-day, and was less in Roman times, than in primitive times and in the Middle Ages, because we, like the Roman engineers, expend a far greater economic effort upon the average of the Road, so that the comparative cost of the bridge is less. In primitive times the bridge was something of a feat, its construction as measured in effort was equivalent to many miles of road, its builder a public benefactor, and its building an event of note. This is so true that in some languages which have come down but little changed from primitive times the word for “bridge” is found to be a foreign word, as though the institution were not sufficiently common before the advent of some civilized conqueror to have acquired a special name; and in all primitive societies the bridge is rare.

This comparatively high cost of the bridge has had certain effects on the history and in the appearance of our roads which are worth noting. In the first place, the bridge tends to be a “gut.” When the throwing of a bridge was equivalent in expense to several miles of the existing road it was a great saving to make it narrow: only one vehicle to pass at a time, with side refuges at the piles when the passage of two vehicles in opposing directions was unavoidable.

Again, bridges tended, especially in times of low economic development, to introduce a sudden high gradient. The elliptical arch was, if not unknown, at any rate very rare before the Renaissance, and where the plain semi-circular arch alone was used a flat bridge involved, if the crossing were of any width, a great number of piles, and therefore an added expense. The difficulty was met in the majority of cases by lessening the number of piles, especially towards the centre, where there was a greater depth, consequently increasing the span there, and consequently, in a semi-circular arch, increasing its height correspondingly. The result was that the bridge introduced a sudden hillock into the Road, and that feature you find all over Western Europe up to quite modern times, with many survivals remaining, especially in Spain. In some of the very early bridges in the poorer districts, or on the less used roads, the exaggeration is fantastic. I know of one over the Gallego, near Huesca, where the pitch is so steep that it baulks a car.

There were particular structures—that of London is an example in point—where the disadvantage of a gradient was avoided at great expense because a mass of traffic and merchandise made it worth while. London Bridge was carried on a great number of arches precisely in order to avoid this element of gradient. A side-effect of this was the blocking of the stream and great difficulty for boats in “shooting” the arches on a tide; but this drawback to river traffic was thought worth while as the price of a level road.

Another reason which often led to the expensive flat stone bridge was its replacing an old wooden pile bridge. The wooden pile bridge had no cause for creating a gradient. On the whole it was cheaper to keep it exactly level, and as low as possible consistent with the rise of the water. Where such a structure had preceded a stone bridge the habit of a level road was continued, even at the expense of many piles and arches.

A third effect of the bridge upon the Road, also due to its comparative expense, was the convergence of roads towards bridges, established or even only planned. You will perpetually find up and down Europe the approaches to a town from two or more directions merged into a common road just at the entry to a bridge, in order to save the expense of two crossings, though at an extra expense of space and time; thus, Abbeville, Caen (a very striking example, with three converging roads on each side of the bridge), London—the chief example in Europe—Saragossa, with the two main roads from south and west converging on its bridge—all “gather” roads after this fashion.

But the effects of the bridge upon the mere trajectory of a road, upon its surface and contour, were far less than were its political and military effects. Though land armies were always tied to roads more or less, it was possible to leave the road for short distances under stress or for the sake of strategy. Cavalry continually did so for great stretches, and infantry could do so occasionally. But a bridge acted like a magnet. The defence of a bridge was the defence of a point which an army in force was always compelled to use, and the term “bridge head”—that is, the holding of the space on the further side of the bridge, thus commanding the passage—is an example of its permanent military function.

A bridge was, for the same reason, a natural place of toll. Merchandise had to use it, and the same requirement of continual repair which often entailed a permanent post at a bridge gave the opportunity for using that post for the raising of taxation. All through the end of the Roman Empire and the Dark and Middle Ages this function of the bridge is most prominent.