Chapter IV. Of what ought to be observed in the building of Bridges, and of the site that ought to be chosen

FORASMUCH as many rivers, by reason of their breadth, height, and rapidity, cannot be F forded, the conveniency of bridges was first thought on. It may therefore be said, that they are a principal part of the way, and that they are but a street above water. They ought to have the same qualities that we have said were required in all other fabricks, that is, to be commodious, beautiful, and for a long time durable, They will be commodious when they are not raised above the rest of the way, and if they be raised, to have their ascent easy; and such place is to be chosen to build them in, as ought to be most convenient to the whole province, or to the whole city, according as they are to be built, either within or without the walls.

Choice ought therefore to be made of that place to which one may go from all parts easily, that is, in the middle of the province, or in the middle of the city, as Nrrocre Queen of Babylon did in the bridge the built over the Euphrates; and not in an angle, where Qu y z: Ver it can be of use only to a few. They'll be beautiful and durable for a long time, if they are made after the manner, and with those measures that shall particularly be mentioned hereafter,

But in pitching on the site for building them, one ought to observe to chuse it so as may give hopes that the bridge there built will be perpetual, and where it may be made with as little expence as possible. That place therefore is to be chosen, in which the river shall be less deep, and shall have its bed or bottom even and durable, that is, of rock or tone, because (as has been said in the first book, when I spoke of the places to lay foun-nations on) stone and rock make very good foundations in waters: be sides which, gulphs and whirlpools ought to be avoided, as also that part of the bottom, or bed of the river, which shall be gravelly or sandy; for sand and gravel being continually moved by the floods, this changes bed of the river, and the foundations being thereby undermined, wou'd of necessity occasion the ruin of the work, But when the whole bed of the river is gravel and sand, the foundations ought to be made as shall be directed hereafter, when I come to treat of stone bridges.

Regard also is to be had, to chuse that site in which the river's course is direct; since the windings and crooked parts of the bunks are subject to be carried away by the water; in such a case therefore the bridge wou'd remain like an island, disunited from the banks: and also, because during the floods, the waters carry into the said windings, all the matter they wath from the banks and fields, which not being able to go directly down, stops other things, and clogging the pilasters, fills up the opening of the arches; whereby the work suffers in such a manner, that by the weight of the water only, it falls in time to ruin.

The place therefore to be chosen for building bridges, ought to be in the middle of the country or of the city, and as convenient to all the inhabitants as possible, and where the river has a direct course, and its bed equal, perpetual, and hallow. But as bridges are either made of wood or of stone, I shall particularly mention the manner of both the one and the other, and shall give some designs of them, both antient and modern,