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for crossing ditches, &c. They are 14 feet long,and 1 foot 6 inches broad. Three troughs arecarried in one waggon. Laid alongside of eachother they form a bridge, for any nature of fieldartillery, across a ditch 12 feet wide; placedacross boats, they form a communication at once,by this simple principle of combining the beamsA B, fig. 27, with the floor, C, fig. 26.

St. Itemi’s carriage-bridge, being floated bycasks, is noticed at page 245, under that head.

Marshal Saxe, in his Reveries, gives a de-scription of a travelling wooden bridge, composedof circular beams, which fold together upon astrong hinge in the middle : when laid, theyform a circular arch of about 36 feet span, abut-ting upon the banks of the ditch or river. Thebridge is transported upon a carriage (which isof no use in the construction) drawn by fouroxen or horses, and laid by poizing it on thebank of the river—hauling the further end to-wards the remote bank, and lowering the whole,gently, as it unfolds; (see plate, Reveries.) Inotice this bridge because it comes from highauthority, but not to recommend its adoption.

A carriage-bridge for infantry, two abreast,was made across the Douro , between Tordesillas and Toro, with the spring waggons of the army.The bottom of the river was hard and even;