Pont du Gard

• 1. Introduction

  ›

  The Pont du Gard stands 48.8 metres above the river Gardon in southern France, carrying nothing but silence now where it once carried 40,000 cubic metres of water every single day. Built in the first century AD, this three-tiered limestone bridge was the tallest point in a 50-kilometre aqueduct system that kept the Roman colony of Nemausus, the city we now call Nîmes, alive and flowing. It was declared a UNESCO World Heritage Site in 1985 on the grounds of human creative genius, testimony to cultural tradition, and significance to human history. How did Roman engineers thread water across a wilderness with almost no slope to work with? What kept this structure standing through floods, wars, and centuries of neglect? And why have writers from Jean-Jacques Rousseau to Henry James found themselves at a loss for words standing beneath its arches?

• 2. A Problem of Altitude

  ›

  Nemausus sat in a geographically awkward position. The plains to the city's south and east held water sources too low in altitude to flow naturally to the city. The hills to the west were too difficult to engineer through. The only viable direction was north, toward the springs of the Fontaine d'Eure near the town of Ucetia, present-day Uzès. The straight-line distance from source to city is only about 20 kilometres, but the aqueduct travels roughly 50 kilometres to reach its destination. That detour was unavoidable. The southernmost foothills of the Massif Central, known as the Garrigues de Nîmes, blocked any direct path. Dense vegetation, garrigue, and deep valleys made the terrain nearly impassable on foot, let alone for a water channel. Tunnelling straight through would have required a passage of between 8 and 10 kilometres, depending on the entry point. A roughly V-shaped course around the eastern end of the Garrigues was the only practical route the engineers could take. The Fontaine d'Eure sits at 76 metres above sea level. The repartition basin at the far end of the journey sits only 17 metres lower. That difference had to move 40,000 cubic metres of water a day across 50 kilometres to supply the 50,000 inhabitants of the city. The overall gradient is only 1 in 3,000. In some sections it falls to as little as 1 in 20,000. The water that left the spring took nearly 27 hours to reach Nîmes.

• 3. Engineering the Impossible Slope

  ›

  The Pont du Gard itself descends just 2.5 centimetres over 456 metres, a gradient of 1 in 18,241. That number is not a quirk; it was a deliberate engineering decision made to keep the bridge at a buildable height. A uniform gradient across the full aqueduct would have pushed the crossing at the Gardon to an infeasible height given the limits of Roman technology. By steepening the gradient in the sections before the bridge and flattening it dramatically in the sections after, the engineers shaved 6 metres off the required height, bringing it down to 48.77 metres above the river. That choice had consequences. The winding stretch between the Pont du Gard and the settlement of St Bonnet required the builders to achieve a fall of only 7 millimetres per 100 metres of conduit. A surveyor called a mensor planned the route using a groma for sighting, a chorobates for levelling, and measuring poles five or ten Roman feet long. His calculations were recorded on wax tablets and later copied onto scrolls. The water conduit at the top of the bridge, called the specus, is roughly 1.8 metres high and 1.2 metres wide. Its interior was plastered with a stucco made from crushed pottery and tile, then coated with olive oil and covered with maltha, a mixture of slaked lime, pork grease, and the juice of unripe figs. This produced a surface smooth enough not to impede the flow and durable enough to last for centuries. The delivery point in Nîmes was the castellum divisorum, an open circular basin 5.5 metres in diameter and 1 metre deep. When excavated, it was found to have once stood beneath a small pavilion decorated with Corinthian columns and a fresco painted with fish and dolphins. Three large drains in the floor may have been used to flood the nearby amphitheatre rapidly enough to stage naumachia, the mock naval battles beloved by Roman audiences.

• 4. Stone Without Mortar

  ›

  The Pont du Gard contains an estimated 50,400 tons of limestone, with a total volume of around 21,000 cubic metres. Some individual blocks weigh up to 6 tons. Most of the stone was quarried at Estel, a site approximately 700 metres downstream on the banks of the Gardon. The local variety, known as Pierre de Vers, is a coarse-grained, soft, reddish shelly limestone that cuts cleanly into precise shapes. Those shapes had to be precise, because the bridge was built almost entirely without mortar or metal clamps. The blocks were cut to fit together by friction and gravity alone. Builders left inscriptions on many stones conveying locations and instructions, including the Latin phrases fronte dextra and fronte sinistra, meaning front right and front left, to guide assembly. The three levels rise from six arches at the base to eleven in the middle tier and originally 47 in the upper tier, now reduced to 35. The bridge is 274 metres long and ranges from 9 metres wide at the bottom to 3 metres wide at the top. Large blocks were deliberately left protruding from the outer face during construction to support the scaffolding and frames that held the arches while they were being built. For the heaviest lifts, the builders relied on a massive human-powered treadmill. Such machines were still being used in quarries across Provence as late as the early 20th century. Émile Espérandieu estimated the total cost of the aqueduct at over 30 million sesterces, the equivalent of 50 years' pay for 500 new Roman legionary recruits. Although the Pont du Gard is celebrated for its appearance, it is not an efficient design. Stacking arches on top of each other uses more material than necessary. Later Roman aqueducts made greater use of concrete and tall, slender piers, as seen in the Acueducto de los Milagros in Mérida, Spain, and the Chabet Ilelouine aqueduct bridge near Cherchell, Algeria.

• 5. Toll Bridge to Ruin

  ›

  From the 4th century onward, successive waves of invaders disrupted the region and the aqueduct's maintenance collapsed. Mineral deposits and plant roots progressively choked the conduit. The deposits left on the conduit walls, built up from layers of dirt and organic material, reach up to 50 centimetres thick on each side. More recent investigations suggest the aqueduct had stopped functioning by around the 6th century, though some parts may have remained in use for longer. The bridge survived not because of care, but because it had another use. In the 13th century the French king granted the seigneurs of Uzès the right to levy tolls on travellers crossing the Gardon over the bridge. That right eventually passed to the Bishops of Uzès, who were also responsible for keeping the structure in good repair. In the 1620s, Henri, Duke of Rohan, led the Huguenot forces against the French royalists and needed to move artillery across the bridge. To widen the passage, he had one side of the second row of arches cut away to roughly a third of their original thickness. The bridge survived, but it was now seriously weakened. By 1703, local authorities repaired the worst of the damage, filling cracks and replacing lost stonework. In 1743-47 the engineer Henri Pitot added a purpose-built road bridge alongside the lower arches to take traffic off the ancient structure. The novelist Alexandre Dumas was critical of this intervention, writing that it was left to the eighteenth century to dishonour a monument that the barbarians of the fifth century had not dared to destroy. By 1835 the writer Prosper Mérimée found the bridge at serious risk of collapse from ongoing erosion.

• 6. Napoleon III and Renewal

  ›

  Napoleon III visited the Pont du Gard in 1850. He had a deep admiration for Roman antiquity and consciously identified with the emperor Augustus. He approved plans drawn up by the architect Charles Laisné, and between 1855 and 1858, with funding from the Ministry of State, the bridge underwent its most substantial renovation. Eroded stones were replaced, some of the piers were reinforced with concrete infill, drainage was improved, and the bridge and the aqueduct above it were physically separated. Stairs were installed at one end and the conduit walls were repaired well enough for visitors to walk through the interior. The bridge had now survived floods, artillery damage, and centuries without maintenance. Three major floods struck in the 20th and 21st centuries alone: in 1958 the entire lower tier was submerged by a flood powerful enough to wash away other bridges in the area; another major flood followed in 1998, and a further flood in 2002 damaged nearby installations. In 1996, with the bridge drawing 1.4 million visitors a year by 2001, the General Council of the Gard département launched a four-year redevelopment project. It was backed by the French government, UNESCO, the EU, and local sources. Vehicles had still been driving across the 1743 road bridge, and illegal commercial structures had accumulated along the river banks. The architect Jean-Paul Viguier designed a new visitor centre on the north bank. The entire surrounding area was pedestrianised, and the commercial clutter was removed. Louis XVI had earlier commissioned the artist Hubert Robert to paint the Pont du Gard for the dining room at the Palace of Fontainebleau in 1786, a commission explicitly designed to link the French monarchy to Roman imperial heritage.

• 7. The Voice of the Stones

  ›

  Jean-Jacques Rousseau first visited the Pont du Gard in 1738 and described it as the only time in his life that an object had surpassed his expectation. He wrote of wandering among the three storeys of the superb edifice and hearing, in the echo of his own footsteps, the strong voices of those who had built it. He said he felt lost like an insect in the immensity, and asked himself why he had not been born a Roman. Henry James visited in 1884 and wrote that the structure was unspeakably imposing and nothing could well be more Roman. He described standing in the twilight as the lonely valley seemed to fill itself with the shadow of the Roman name, as if the mighty empire were still as erect as the supports of the aqueduct. Joseph Méry, writing in his 1853 book Les Nuits italiennes, contes nocturnes, described the Pont du Gard springing up from a desert landscape as the most magnificent object that civilization had created for the glory of the fine arts. Hilaire Belloc, writing in 1928, admitted a great reluctance to praise what had been praised too much, but confessed that when one sees the thing, all that is said of it comes true. He found in it a quality of isolation, dignity, and weight that he called awful in the older sense of the word, and suggested that a man suffering from the unrest of his time might do worse than camp out for three days fishing and bathing in its shadow. The bridge had also attracted journeyman masons on the Compagnons du Tour de France, the traditional circuit of France by craftsmen, who visited to study its masonry and left their names carved into the stonework. The castellum divisorum that once received the water at the other end of the journey is still standing in Nîmes, its ten outlet pipes and three floor drains intact, waiting for the flow that stopped roughly fifteen centuries ago.