A book of bridges

by Walter Shaw Sparrow

1. This bridge from Bhutan has the same technique as the cantilever bridges of Kurdistan ([p. 74]); but the gateway towers mark an advance. They are militant works, partly because they control the traffic, and partly because they are open below the eaves for archery and for other defensive warfare. Brangwyn suggests that gateway towers of this kind may have been brought to India by Darius Hystaspes (512 B.C.) or by Alexander the Great (327 B.C.). On this point there is no evidence. On the other hand, there seems to be no doubt that the timber gateways on Roman bridges in England, as in Gaul, were prepared for defence, though their main use was to limit the freedom of a public thoroughfare, invariably after sunset, and during the day in times of unrest. This was the first aim of defensive bridges, so the gateway towers in Bhutan are suggestive things to study. They are too light in structure to give us an idea of the bold and stern gateways built by the Romans with newly-felled trees; but yet they help us to realise vaguely what every young civilization must have done when it learnt from a free use of bridges that foes as well as friends were eager to pass without danger across rivers.

PRIMITIVE TIMBER BRIDGE IN BHUTAN, INDIA

Again, the earliest defensive bridges had another point in common with the primitive carpentry of Bhutan: they were made with tree-trunks resting on supports, and, when necessary, a part of their footways could be removed. Diodorus Siculus wrote a flaming account of a great bridge built by Semiramis over the Euphrates, rather more than two thousand years before the birth of Christ. After making due allowance for the frolicsome legends with which ancient history is enlivened, there are things worth noting in the enthusiasm of Diodorus. Herodotus attributed the same bridge not to Semiramis but to Nitocris, so evidence can be drawn from two authors. Pontists gather from the evidence that stone piers were connected by planks, which were taken up at night, just as the central part of a bridge in Bhutan could be removed as a military precaution. Diodorus draws entertaining pictures, and tries to prove that bridge-building was far advanced twenty centuries before our era began. If Semiramis collected architects and craftsmen from all the known civilizations, until at last she had at her beck and call a great host of capable servants, it is not surprising that she was able to build a fine bridge as well as to enlarge Babylon. The piers were grounded in deep water; their ends were protected by triangular buttresses; their stones were clamped together with thick bars of iron, which were soldered into the stones with molten lead. As for the superstructure, it was thirty feet wide, and all of wood—cedar, and cypress, and palm tree. In all this, probably, there is some exaggeration, but a famous bridge did exist at Babylon, and a combination of timber with stone piers was the most logical development from the simplest natural bridges—the fallen tree and the bridge of stepping-stones. Also it is likely enough that metal clamps were employed; iron was in vogue, and by using it in stonework under water an architect would feel less mistrustful of his cement and less anxious about the risks of floods. Further, it is quite probable that the entrance at each side was protected by a sort of drawbridge, because the times were lawless. Semiramis herself was put to death by her son Ninyas, and Ninyas in his turn was murdered.[119]

An important timber bridge with stone piers belongs to a handicraft more advanced than that in the bridges of Bhutan; it comes between the primitive inspiration of the Bhutan carpenters and the simplest arched bridges with plain gateway towers. It has not yet vanished from Europe, for a Gothic example exists at Thouars, in Deux-Sèvres, France, according to a photograph sold by Neurdein, of Paris. Another example crosses the Guadalaviar above Albarracin, in Aragon; and let us remember also that the tree bridge resting on stone piers has influenced some metal viaducts, such as Runcorn Bridge, near Liverpool, dating from 1868. In principle the construction is the same, timber being displaced by metal. At the end of its approach arches, where the metalwork begins, Runcorn Bridge has two gateways, each with twin turrets, and a great display of battlements and of machicolations. Although this make-believe of war has a farcical bad taste, like the assumed erudition that keeps dummy books in a library, yet Runcorn Bridge has a well-defined interest: it mimics a phase of military architecture which was evolved from such carpentry as to-day we find in Bhutan.

DEFENSIVE BRIDGE AT SOSPEL

2. Gateway Bridge at Sospel, in the Italy of France. This drawing illustrates very well the transition from the primitive bridges of Bhutan to a simple arched bridge guarded by a gatehouse of control. It is a poor little house, its architecture being less intelligent than that in the Bhutan gateway towers. In these there is cleverness enough to prove that the bridge represents a stale old custom which has lagged behind the advance of handicraft, whereas the bridge at Sospel is far in advance of the tawdry little gatehouse. A span separates the gatehouse from the town, and the roadway is not on the same level above both arches.