terminating the second story. The total height, according to the same author, is 161 feet ; namely, 66 feet for the first range, 66 feet for the second range, and 21J feet for the third range to the top of the flags covering the water channel ; the width of the bridge is 21 feet at the first range, 16 feet on the second, 10 feet on the third ; this forms a considerable offset on each stage ; the five piers of the first range of arcades were formed with salient angles or bees. The division of the arches on the first and second stories is the same ; the middle arch of the first range, under which the river passes, and which is the centre of the entire aqueduct, is 70 feet in diameter ; three on each side are of smaller dimensions. All the arches on the third range or story are equal, being 15 feet in diameter ; the piers of the first and second series of arches are 15 feet in front ; those of the third range vary according to the diameter of the arches of the range beneath them, four arches of the third range corresponding with the middle or water way of the lower story. As the two mountains forming the valley of Gardon are not of equal height at the points in the line of aqueduct, that on the left side of the river being lower than the level of the aqueduct, while the right side is more elevated, the conduit on one side is carried onwards by continuing the third range of arches, and on the other side, the range terminates in the side of the mountain. The Pont du Garde is constructed entirely with hewn stone ; no rubble work is introduced even into the filling up of the piers, or spandrils of the arches. The masonry PRELIMINARY ESSAY. 31 has been finished and put tog-ether without lime, or any other kind of cement, and owes its stability to the mass of each block, and the precision of the faces in their beds and joints. The canal of the aqueduct is in fact the only part which is not constructed with hewn stonesr being made with a sort of jointed rubble on the outer and inner faces of the canal, but of the common rubble in the filling up. This work, where the cement has not been sparingly used, forms a mass absolutely impenetrable to any passage of the water. 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. This interesting monument of ancient Roman magnificence was demolished at its two ends, some time about the beginning of the fifth century, by the barbarians who then besieged Nismes, and who, by this means, endeavored to force the citizens to surrender. It remained in this state until the beginning of the eighteenth century, when the Duke de Rohan, in order to make a passage for his artillery, perforated the piers of the second arcade, and by some other operations directed to the same end, the Pont du Garde was rapidly falling to pieces. Considerable rents in the walls, and deviations from the perpendicular, exciting public attention, the provincial States took the matter into consideration, and by a series of judicious repairs, they succeeded in restoring this ornament of