3. Pont du Gard Aqueduct, Nimes, France
Roman architects and hydraulic engineers built this three level, 360 meter-long and 50 meter-tall bridge in Nimes, France during the first century A.D. Mainly, it was built with tons of soft, yellow limestone from a local quarry. Crossing over the Gardon River, it supplied Nimes, formerly known as Nemausus, with water. The bridge’s design is an engineering feat; the structure’s largest arch gap is 25 meters which is one of the greatest in the Roman world.