Chap. XXIII.

TIMBER BRIDGES.

1340

us by Julius Caesar of one over the Rhine: Alberti, Palladio, and Scainmozzi, have eachattempted to design its form; but their ideas upon the subject differ materially.

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.*7' aoriininjpi.

Fig. 2171.

c^sar’s bridge.

Caesar tells us that two pieces of timber 18 inches square, after being pointed at theirlower ends, were sunk into the river, and afterwards driven 2 feet distance from each otherby means of machines ; these piles were inclined a little ; two others were driven at a dis-tance of 40 feet opposite them, inclining in the contrary direction; these two pairs of piles

Fig. 2172.

were united by a transverse beam at the top, which was in thickness 2 feet, and properlysecured: on these were laid joists in the direction of the breadth of the river, which werecovered with hurdles to sustain the road. On the side below the stream inclined pileswere driven, which supported the bridge against the force of the current, and above thebridge were others, to protect it from injury against floating masses, as trees or boats: itwas completed, and. the troops were enabled to pass over it in ten days.

Alberti fastens the girders to the heads of the piles by ropes instead of two bolts(binis Jibuti*)., as perhaps the text implies: Palladio has introduced two pieces of timberfor their supports, halved and bolted into the sides of the inclined piles: Scammozzigives a double tie of cordage: Perrot d’Ablincourt attaches these cross-beams or girdersby means of several enterties, which seems justified by the text.

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