Pont du Gard, France
The Pont du Gard is an ancient Roman aqueduct that crosses the Gardon River near the town of Vers-Pont-du-Gard in southern France. The Pont du Gard is the highest of all elevated Roman aqueducts, and, along with the Aqueduct of Segovia, one of the best preserved. It was added to UNESCO's list of World Heritage Sites in 1985 because of its historical importance. The bridge has three tiers of arches, stands 48.8 m (160 ft) high, and descends a mere 2.5 centimetres (1 in) â€" a gradient of only 1 in 18,241 â€" while the whole aqueduct descends in height by only 12.6 m (41 ft) over its entire length, which is indicative of the great precision that Roman engineers were able to achieve, using simple technology. The aqueduct formerly carried an estimated 40,000 m3 (8,800,000 imp gal) of water a day to the fountains, baths and homes of the citizens of NÃ®mes. It may have been in use as late as the 6th century, with some parts used for significantly longer, but a lack of maintenance after the 4th century led to clogging by mineral deposits and debris that eventually choked off the flow of water.