The method he adopted in building the bridge was as follows. He took a pair of piles a foot and a half thick, slightly pointed at the lower ends and … - Gaius Julius Caesar

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The method he adopted in building the bridge was as follows. He took a pair of piles a foot and a half thick, slightly pointed at the lower ends and of a length adapted to the varying depth of the river, and fastened them together two feet apart. These he lowered into the river with appropriate tackle, placed them in position at right angles to the bank, and drove them home with pile-drivers, not vertically, as piles are generally fixed, but obliquely, inclined in the direction of the current. Opposite these, forty feet lower down the river, another pair of piles was planted, similarly fixed together, and inclined in the opposite direction to the current. The two pairs were then joined by a beam two feet wide, whose ends fitted exactly into the spaces between the two piles forming each pair. The upper pair was kept at the right distance from the lower pair by means of iron braces, one of which was used to fasten each pile to the end of the beam. The pairs of piles being thus held apart, and each pair individually strengthened by a diagonal tie between the two piles, the whole structure was 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. A series of these piles and transverse beams was carried right across the stream and connected by lengths of timber running in the direction of the bridge; on these were laid poles and bundles of sticks. In spite of the strength of the structure, additional piles were fixed obliquely to each pair of the original piles along the whole length of the downstream side of the bridge, holding them up like a buttress and opposing the force of the current. Others were fixed also a little above the bridge, so that if the natives tried to demolish it by floating down tree-trunks or beams, these buffers would break the force of the impact and preserve the bridge from injury.