The valley between Soncieu and Chaponost is about 200 feet deep. Five ranges of arcades, placed one over the other, for a length of 2400 feet, conducted the water across the valley the valley through which ;

the river d'Izeron flows, between Chaponost and St. Foi, is nearly 300 feet deep, and was crossed by a series of arcades having eight ranges in height. The third valley, formed by the small hill of St. Foi, and that of Fourvieres, had three ranges of arcades.

These prodigious substructions must have occasioned an outlay so enormous, as under almost any circumstances would have completely arrested the completion of the undertaking ; and the more so, as these valleys were neither all, nor the greatest across which th*

38 PRELIMINARY ESSAY.

water had to be conducted. The resources of the architects here become conspicuous, in their substitution of leaden pipes, forming syphons, already described, which were laid at an expense comparatively trifling, to what must have been incurred by following the other and more usual method. In describing the passage of the valley of the Garon, the aqueduct arriving at the summit of the hill, was stated to deliver its water into a tank, or reservoir, placed in a square tower. This reservoir, fourteen feet long by four and a half feet wide, is seven feet high to the summit ol its arch ; the walls are four and a half feet high to the springing of the arch, and two feet three inches thick. The arch is pierced in the centre by an opening two feet square, which serves as a passage into the reservoir. The bottom is lined with a coat of cement, six inches thick, with a curve at the angles of concourse of the sides and bottom ;