Chap. IV.
ROMAN.
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of literature, moderate at his table, and partial to men of genius from amongst whomUlpian was selected to be his constant companion.
The Aqueduct at Nismes, or the Pont du Gard , was, perhaps, the earliest constructed by theRomans out of Italy, and is supposed to have been executed by Agrippa , who was governor
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of that city in the time of Augustus , and declared curator perpetuus aquarum. Its perfectarrangement affords us the best means of judging of such works.
It has three tiers of arches, one above the other; the lowest, under which the riverGardou passes, is composed of six arches, the second of eleven, and the upper or thirdtier of thirty-five, besides two openings made at the side, at the time of the invasion ofGaul . The arches are semicircular, and rest upon piers more or less elevated. Above theupper row was the conduit for the water, which passed the valley of the Gardon at aheight of more than 157 feet above the river below.
The length of this splendid monument at the level of the string course surmounting thefirst tier is 562 feet, and at the level of the second string course 885 feet; it is nearly thesame length above the crowning stones of the aqueduct, between the extremities wherebroken down.
Tlie total height is 161 feet, viz. 66 feet for the first story from the bed of the river tothe first string course, the same to the second string course, and 29 feet to the top of thestones which cover it. The divisions of the arches and piers of the first and second storiescorrespond; the largest arch of the first story, under which, when there is little water in it,it generally passes, is the centre of the monument, and the second from the left bank of theGardon. On the first and second story, on each side, are arches of a smaller space, whichare succeeded by others still less. The difference in the span of these arches, and their allbeing semicircular, obliged their springing to commence at different levels, which has asingular effect. The large arch through which the river passes is 80 feet 5 inches indiameter; the three on the right side are 63 feet, and the smaller are 51 feet. All the archesof the upper story are equal in span, 15 feet 9 inches: their piers vary in width, and donot come immediately over those of the two stories below ; consequently, in this tier thereis no symmetry maintained with those beneath them, nor are the perpendiculars kept.
The thickness of the Pont du Gard , from the face of one side to that of the other, is atthe first story 20 feet 9 inches, at the second story 15 feet, at the third 11 feet 9 inches.Each story forms a considerable set-off, three feet nearly on each side of the first story, and1 foot 6 inches at the second, where the string course or cymatium was increased a littlemore than a foot in its projection, to allow foot passengers to traverse the valley withmore facility.
'Hie lower piers are strengthened and protected by buttresses of a triangular plan, whichdirected the waters of the valley in time of floods. The construction of the Pont du Gard exhibits great skill ; the stones are all laid according to their natural beds in the quarry,and their dimensions are considerable: they were brought from the neighbourhood, onthe left bank of the river, and are of the same quality as those employed in the amphi-theatre at Nismes. Corbels or projecting stones are left in various parts, for the purposeof supporting the centres and scaffolding, which were not removed, that they might be ser-viceable for after repairs.
The foundations were established upon a rock 6 feet above the bed of the river, and thethickness of the piers is formed of only two or three stones of large dimensions. Thecourses are in general 2 feet in height. The key-stone of the large arch is 5 feet 3 inches,and that of the others 5 feet in depth ; those of the arches of the upper story 2 feet 7 inches.
The lower arches are formed of four separate rings in their soffites, those of the rangeabove of three, and those of the upper or smaller range of single rings or courses of voussoirs :
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