it could support itself. The first voussoirs were placed at the springing (the part of the pier carrying the arch) and others added until a keystone locked the arch at the center.

Some scattered remains of the aqueduct survive: a 55-foot-long (17-meter) three-arched bridge near Bornègre; a few exposed sections of the subterranean channel; another raised section near Vers; sections of tunnel; and the Pont de Sartanette, spanning about 100 feet (32 meters) over a small valley. The Pont du Gard itself continued in use until the ninth century, after which it was abandoned. Some of its stones were subsequently plundered by builders with less noble projects in mind, but generally it has survived human intervention. The bottom tier has long been used as a pedestrian thoroughfare, and in the Middle Ages stones were removed from one side of the piers so that laden mules could pass. In 1702 local authorities began renovations, attempting to close cracks, filling in ruts and building corbels to help support the road. The removed stones were replaced, and in 1743 a new bridge was built beside the lowest tier, widening the “roadway” for vehicular traffic. Overawed by the majesty of the structure, Napoléon III ordered its restoration (1855–1858), and subsequent projects have consolidated the mighty piers and arches.

As noted, the Pont du Gard was given World Patrimony status by UNESCO in 1986, and two years later the Regional Council of Gard began a historical and ecological protection program. In 1991–1992, fretted stones in the bottom level were replaced and waterproofing was improved; similar work continues on the second tier. Currently, the monument attracts more than 1 million visitors annually. There is growing concern that the Pont du Gard will be further threatened as those numbers increase—an example of the tension that everywhere exists between conservation and tourism.

Further reading

Aicher, Peter J. 1995. Guide to the Aqueducts of Ancient Rome. Wauconda, IL: Bolchazy-Carducci.

Fabre, Guilhem, et al. 1992. The Pont du Gard: Water and the Roman Town. Paris: Presses du CNRS.

Hauck, George. 1988. The Aqueduct of Nemausus. Jefferson, NC: McFarland.

Pontcysyllte Aqueduct

Denbighshire, Wales

At Pontcysyllte (Welsh for “connecting bridge”) the Llangollen Canal crosses the River Dee at a height of 120 feet (36 meters) by means of a breathtaking aqueduct that marches more than 1,000 feet (306 meters) over the valley on nineteen slender, tapering (and partly hollow) masonry piers. Built between 1795 and 1805, the graceful structure remains the highest navigable canal aqueduct ever built. Besides its own weight it supports 1,680 tons (1,524 tonnes) of water. Pontcysyllte Aqueduct has been correctly identified as “one of the heroic monuments of the Industrial Revolution,” and the novelist Walter Scott asserted that it was the finest work of art he had ever seen.

Part of Britain’s 2,000-mile (3,200-kilometer) canal network, the spectacular Shropshire Union Canal—really a collection of canals built by various companies at different times—stretches 67 miles (107 kilometers) from the English Midlands town of Wolverhampton to the River Mersey. The original ambitious plan to link the Mersey and Severn Rivers was never achieved. The first stage, the Chester Canal from the River Dee in Chester to the town of Nantwich, was completed in 1779. Between 1796 and 1806 the Ellesmere Canal (later renamed the Llangollen Canal), fed largely by the Dee at the Horseshoe Falls, was built to connect Wrexham’s ironworks and collieries with Chester and Shrewsbury. Joining the Chester Canal to Ellesmere Port in the Mersey Estuary, it reached as far as Llantisilio near Llangollen in North Wales. It is probably the most beautiful canal in Britain.

At Pontcysyllte the Llangollen Canal is channeled over the Dee Valley in a 12-foot-wide (3.6-meter) trough made of cast-iron plate and supported by four arched iron ribs spanning 44 feet (13.6 meters) between the tall piers. The water level comes to within a few inches of the top of the trough, and because a towpath is cantilevered over the surface, the navigable width for long boats and barges is reduced to about 7 feet (2 meters). There is a safety railing on the towpath side, but on the opposite side there is a sheer drop to the valley floor, 120 feet (36 meters) below.