The inside facing of the walls, and the bottom hollowed in the form of an arc of a circle, were covered with a coat of cement about two inches in thickness, composed of quicklime, fine sand, and pulverised bricks. This cement is at the present day of a consistence equal to that of the hardest and most compact stone, and without the slightest crevice or flaw to be any where seen in it. This first coat of cement was covered with a second

layer of mastic, very fine and very thin, of a deep, dark, red color. The width of the canal between the outer coats was four feet, and its height the same.

The general declivity of the bed of the aqueduct was about four centimetres for one hundred metres, or one and one-third inches to three hundred and twenty-eight feet. The aqueduct has been constructed with the same care throughout its great length, the only difference being that, in the parts exposed, the aqueduct was covered with slabs, and in the subterranean portion it was covered with a semi-circular arch, of a species of rubble roughly squared in the joints, nearly two feet in thickness.

In examining the water channel, a strong concretion is observable, adhering to the cement on the sides and bottom. This petrifaction is nearly twenty-nine centimetres thick, or 11 and one-third inches, and from this it appears, that the general height of the stream of water in the channel was about three feet nine inches.