The bridge of Avignon was begun in the year 1176, and finished in 1183, probably under the direction of St. Benezet and the fraternity of hospitallers, over whom he presided ; it consisted of 18 arches, and was about 1,000 yards in length. The roadway was so narrow, that two carriages could not pass each other in any part ; this had caused it to be deserted by all but foot-passengers long before its destruction, which happened in 1699, by one of those violent inundations com mon to the Rhone. Many of the ruinous-decayed arches still remain.
The city of Venice has nearly 500 handsome bridges of one arch, and various sizes, over the canals, &c. ; most of them are of white stone, similar to that with which the streets are paved, without any balusters or fence on either side. Of these the principal is the Rialto, esteemed, when erected, a master piece of art. It was begun in 1555, and finished in 1591, after a design of Michael Angelo, and consists of one bold flat arch, nearly 100 feet wide, and only 23 in height from the level of the water. Its breadth, which is 43 feet, is divided into three narrow streets, by two rows of shops : the middle street is the widest, and in the centre there is an arched aperture, by which the three streets communicate with each other. At each end of the bridge is an ascent of 56 steps, and the prospect from its summit is both lively and magnificent. The foundation extends 90 feet, and rests upon 12,000 elm piles ; the whole exterior of the bridge, as well as of the shops, is of marble. The building cost the Republic 250,000 ducats.
The most stupendous and magnificent work ever executed in the department we are now speaking of, is the aqueduct bridge of Alcantara, near the city of Lisbon. It was begun in the reign of John V. king of Portugal, in the year 1713, and was finished on the sixth of August, 1732, under the superintendence of Brigadier Manse] de Maya. The aque duct commences at a spring near Riheira de Caranque, about three leagues and a half from Lisbon, to which city the water is conveyed for the supply of the inhabitants. The aqueduct passes subterraneously through the hills, receiving in its course the waters of several springs, and stretches across many valleys on the tops of magnificent ranges of arches, of which that crossing the vale of Alcantara is the principal. When the water emerges from its subterraneous passage, it is received in two channels on the tops of these arches, each about 12 inches deep ; it generally flows at about the depth of seven inches, yielding an abundant supply for the city and its environs. The interior height of this building is 13 feet, and between the streams is a paved walk or foot-path. The subterraneous passages are continued of
the same height and width throughout the whole extent of the works, and are lighted and ventilated by openings to the surfitce of the hills through which they pass. Over each of these openings are turrets or square towers, with strong latticed windows, to prevent mischievous persons from throwing stones, &e., into the aqueduct. These turrets are 16 in number, each 16 feet square, and rising 23 feet six inches above the roof of the aqueduct ; the number of win dows is '79, each three feet seven inches long, by 13 inches wide, railed with iron and latticed with bars. Beneath every second turret is an arched doorway into the aqueduct. The wate•-channel under the grand arch is about 24 feet in width, and seven feet in depth ; but this channel is dry, except in very rainy seasons. There is, indeed, a small stream con • • stantiv running through the vale of but it is conveyed by a very narrow channel under the pavement beneath the grand arch, and then continues its course through the valley in a stream between two and three feet wide, till it falls into the Tagus, about two miles below. This remark able structure consists of 35 arches, of various dimensions. The eighth is the grand arch, which is 108 feet five inches in the span, and 227 feet in height: the other arches vary from 21 feet ten inches, to '72 feet in width. The total length of the piers and arches is 2,464 feet. The expense of erecting this work, and keeping it in repair, has hitherto been defrayed by the trifling rate of one rey on every pound of meat sold in the markets of Lisbon.
In France, besides the Roman structures already noticed, there are many bridges of more recent date, remarkable both for their size and the boldness of their construction: among these may be mentioned the bridge of Neuilly, built between the years ] 76S and l'750, by N. Perronet. It crosses the Seine, on a line with the grand avenue of the Champs Epees, in the front of the Tuilleries; it is level on the top, and consists of five equal arches, 120 feet French (128 feet English) in the span, with a rise of 30 French feet (32 feet English). The piers are 14 feet thick, and the bridge itself 48 feet broad. The arches, which are elliptic, are composed of 11 arcs of circles, of different diameters : the upper portion of the arch was formed with a circle of 160 feet radius, which, by its settlement during the building and after remo ving the centres, became flattened to an arc of a circle of 259 feet radius, differing so little from a platband, that the rise of the curve in a length of 33 feet, amounts to no more than six inches nine lines.