Athena Review I,4: Pont du Gard Aqueduct

Athena Review Vol.1, no.4

The Aqueduct at Pont du Gard

The impressive remains at Pont du Gard of the largest of several intact sections of the Roman aqueduct supplying Nemausus (Nîmes) may be seen 18 km NE of Nîmes. The famous three-tiered bridge, spanning 275 m over the Gardon valley, was constructed of locally quarried limestone blocks weighing up to six tons, fitted together without mortar and secured with iron clamps.

This monumental engineering feat, begun after a visit to Gaul in 19 BC by Agrippa, son-in-law of Augustus, was probably completed during Trajan's reign (AD 98-117). Although Nîmes had a spring at the shrine of Nemausus, the city soon outgrew this local supply. Water was thus brought about 50 km from the springs of Fontaine d'Eure at Uzès to the stone castellum (storage basin) at Nîmes. At least 20,000 m3 (44 million gal) were then distributed daily through ten main pipes to the baths, public buildings, and houses of the city. This supplied 400 liters of water per person per day, considered adequate by today's standards. Along the aqueduct's winding course flanking outcrops of the Massif Central, the elevation drops only 17 m with an average pitch of 1:300. This shallow incline of 34 cm/km, achieved through a combination of 35 km of subterranean channels linked by low bridges, was steepened just before the Gardon valley to reduce the height of the bridge as much as possible.

The lowest of the Pont du Gard's three tiers is 142 m in length and contains six arches 22 m high. The middle tier (fig.1) has eleven arches each 20 m high, spanning 242 m. The third and topmost row of 35 arches (seven m high) covers 275 m and carries the all-important water channel (1.22 by 1.75 m). Some of the blocks along the two lower tiers protrude from the face to allow placement of scaffolding during repairs. One estimate of the aqueduct's construction costs (Esperéndiu 1926) was 30 million sesterces, equal to 50 years' pay for 500 legionary officers.

[Fig.1: Pont du Gard (photo: Athena Review).]

Since its ancient construction, the Pont du Gard has undergone periodic restorations. Stones removed in the Middle Ages to ease crossings were later replaced in 1743 when a bridge was built next to the first tier. Projects from 1855 through the 20th century have replaced stones as needed to consolidate the aqueduct's walls and vaults. In 1991-92, stones of the lowest tier were replaced and water proofing improved. A similar project is currently underway for the second tier, designed to reduce hazards to tourists and to ensure the future of the monument now entering its third millennium. Although 300 cubic meters of stone (weighing about 800 tons) will be replaced, this represents only 5% of the total mass of Pont du Gard.

Additional remains of the Nîmes aqueduct (fig.2) include a 17 m long bridge of three arches near Bornègre, where the underground water channel first emerges and crosses a stream. Five km west of this bridge is another exposed section of the subterranean channel. Further along, near Vers, is a raised portion of the aqueduct called Pont Rue, of which about 700 m survive in two sections flanking the road. Over the centuries, these have been depleted to their foundations for building stone. Very near Pont du Gard is the Pont de Sartanette, taking the aqueduct 32 m across a smaller valley. Here the grade is a mere 7 cm/km and the channel was narrowed and heightened to compensate. Further down, just N of Sernhac are two sections of aqueduct tunnel 66 and 60 m long with the marks of ancient pickaxes still visible. The last section to be seen before reaching Nîmes, found while constructing the railway to Remoulins, lies just to the south of Sernhac. A testament to the durability of Roman engineering came during a 1958 flood, which submerged the entire lower tier of the Pont du Gard. While a modern bridge downriver at Remoulins was wrecked, the Roman structure remained undamaged.

[Fig.2: Map of the Nîmes aqueduct (after Broward 1996).]

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