The size of the channel-way is the following: 4 feet wide and 5⅓ feet high, except where the top is covered with an arch, in which case it is 7½ feet high in the interior.
The descent of the Aqueduct is 1 foot in 2500 feet, or 2-11/100 feet per mile.
The water which flowed in this Aqueduct formed a deposit upon the sides, of lime, until nearly half the channel was closed; this deposit amounting to a thickness of 11 inches on each side. By the height of this deposit it has been ascertained that the water flowed generally with a depth of 3¼ feet.
The pont du Gard is that part of the Aqueduct of Nismes which crosses the deep valley in which runs the Gardon or Gard. This part, considered alone, is one of the noblest monuments built by the Romans among the Gauls. It is composed of three ranges of arches one above another. The first range, under which the Gardon flows, is formed by 6 arches; the second by 11, and the third by 35, all of which are semicircular; supported upon piers of greater or less height.
The channel in which the water flows is upon the top of the third range of arches, and is 160 feet above the water of the river. The whole length of this bridge is about 900 feet.
The bridge of Gard having been broken down at the two extremities, at a period very remote and uncertain, it is thought that this destruction may be attributed to the Barbarians who invaded the country of Nismes a short time after their first invasion, which is fixed at the commencement of the fifth century, about the year 406, and it is supposed that by this means they would deprive the inhabitants of Nismes of the water furnished by the Aqueduct, and force them to yield. But by this supposition, which is very probable, the water had been running in this Aqueduct for more than four centuries; and this structure which has been out of use during fourteen hundred years, is still in such a state of preservation that it could be restored without a very great expenditure of money.
The Ancient Aqueducts of Lyons.
Nothing gives a better idea of the splendour of the city of Lyons under the reign of the first Roman Emperors, than the remains of the ancient monuments. We see there at the present day, remains of temples, of palaces, of amphitheatres, of basins for mock sea fights, of baths and of many Aqueducts, of which three were constructed under the reigns of Augustus, of Tiberius and of Claudius, for conducting water to that part of the ancient city situated upon the mountain.
The first and the most ancient of these Aqueducts, constructed by Mark Anthony, brought the waters from Mount-d’Or, by means of two branches which embraced that group of mountains.
The water furnished by the first Aqueduct having been found insufficient, they constructed a second one to bring the water of the Loire.