Pont du Gard

The Pont du Gard crosses the Gardon river in the commune of Vers-Pont-du-Gard, in the Gard department of southern France, a short distance from the small town of Remoulins and some twenty-five kilometres north-east of Nîmes. It is not a bridge in the ordinary sense. What survives is the centrepiece of a Roman aqueduct, and the arches were built not to carry people or carts but to hold a covered water channel level as it crossed a river gorge. Three tiers of arches lift that channel 48.8 metres above the water, which makes the Pont du Gard the tallest aqueduct bridge the Romans ever raised anywhere in their empire. The lower tier carries six arches over 142 metres, the middle tier eleven arches over 242 metres, and the top tier originally held forty-seven small arches along some 360 metres, of which thirty-five remain across a length of about 275 metres. The structure tapers as it rises, from roughly nine metres thick at the base to three metres at the summit, and the widest of the lower arches spans 24.52 metres, set deliberately over the main channel of the river.

The bridge only makes sense as part of the system it belonged to. The aqueduct ran a little over fifty kilometres from the Fontaine d'Eure, a spring near Uzès, to the distribution basin at Nemausus, the Roman city that became Nîmes. The direct distance between the two points is barely twenty kilometres; the extra thirty were spent contouring around the hills of the garrigue because the engineers had almost no height to spend. The total fall from source to city was about twelve metres, an average gradient of roughly one in three thousand, and across the Pont du Gard itself the channel drops just 2.5 centimetres over 456 metres. Holding that tolerance over fifty kilometres of limestone country, with the surveying instruments available in the first century, remains the most impressive thing about the monument, and it is invisible to anyone standing beneath it. Water took close to twenty-seven hours to travel from the spring to the city, and the aqueduct is estimated to have delivered in the order of 200,000 cubic metres a day to the fountains, public baths and private houses of Nîmes.

Dating has shifted over time. The aqueduct was long attributed to Marcus Agrippa and placed around 19 BC, but the archaeological evidence now points to the middle of the first century AD, most likely between 40 and 60, and the earlier attribution has been set aside. Estimates suggest that between eight hundred and a thousand workers were employed and that the bridge took roughly fifteen years to complete, at a cost in the region of thirty million sesterces. The stone is a shelly local limestone, the pierre de Vers, quarried a few hundred metres downstream; something like fifty thousand tonnes of it went into the structure, with individual blocks weighing as much as six tonnes. Those blocks were dressed so precisely that the visible masonry needed no mortar at all and holds together by friction and weight alone. The builders left projecting stones and slots in the piers to carry the scaffolding and the lifting gear, and never bothered to trim them off afterwards, so the ledges are still there. Quarrymen's marks and the assembly numbers cut into the voussoirs can still be read on the stonework, which is why the monument is valued as much for what it reveals about Roman working methods as for its silhouette. The channel it carries is about 1.8 metres high and 1.2 metres wide, floored in concrete and originally lined with a stucco sealed against leakage.

The aqueduct worked for something close to five centuries. From the fourth century onwards maintenance faltered, calcium carbonate deposits thickened inside the conduit and roots worked into the masonry, and by around the sixth century the channel had ceased to carry water. The bridge itself survived because it found a second use: through the Middle Ages local lords and bishops kept it up as a toll crossing, charging for passage along the lower tier, and that revenue paid for repairs at a time when other stretches of the aqueduct were being quarried away for building stone. The second row of piers was cut back over the centuries to widen the roadway, which weakened the structure badly, and in 1743 to 1747 the engineer Henri Pitot built a proper road bridge flush against the lower tier to take the traffic off it. A full restoration followed a century later, directed by the architect Charles Laisné between 1855 and 1858 under the patronage of Napoleon III, which replaced damaged stone, filled the piers with concrete and improved the drainage of the upper channel.

The Pont du Gard was inscribed on the UNESCO World Heritage List in 1985 under criteria (i), (iii) and (iv), cited as a masterpiece of Roman technique and as one of the most informative surviving monuments of early imperial construction practice. It now receives in the region of 1.4 million visitors a year, which places it among the most visited monuments in France. Cars were removed from the immediate surroundings in 2000 and the banks were redeveloped with a visitor centre, a museum devoted to the aqueduct and to Roman hydraulics, and marked paths through the garrigue on both sides of the river. Visitors can walk across the lower tier, follow traces of the buried channel in the surrounding countryside, and in summer swim and paddle in the Gardon beneath the arches, which is the view most photographs are taken from. The stone shifts colour through the day, from pale grey in flat light to a deep honey at the end of the afternoon, and the scale only registers properly from the riverbank, where the six lower arches turn out to be roughly the height of a fifteen-storey building.