Pont du Gard

Built by Roman engineers around the middle of the first century AD, the Pont du Gard carried the aqueduct of Nîmes across the Gardon river gorge, part of a 50-kilometre channel that supplied the Roman city with an estimated 40,000 cubic metres of water a day. Rising 49 metres in three tiers of arches, it is the tallest surviving Roman aqueduct bridge, its precisely cut limestone blocks—some weighing six tonnes—assembled without mortar. The channel's gradient drops only about 34 centimetres over its final kilometres, a marvel of ancient surveying. Abandoned after Rome's fall, it survived partly because it doubled as a toll road bridge through the Middle Ages.