There is a moment, approaching the Pont du Gard from the riverbank below, when the structure stops looking ancient and starts looking inevitable. Three tiers of limestone arches rising 49 meters above the Gardon river in southern France, built without mortar, without iron clamps, without any binding agent beyond the weight of precisely cut stone on stone. It was constructed around 50 CE to carry water 50 kilometers from springs near Uzès to the Roman colony of Nemausus — modern Nîmes. It has been standing for nearly two thousand years. It looks like it intends to stand for two thousand more.