The Pont du Gard is an ancient Roman aqueduct that crosses the Gardon River in southern France. The bridge is part of the Nîmes aqueduct, a 50-kilometre system built in the first century AD to carry water from a spring at Uzès to the Roman colony of Nemausus (Nîmes). Because of the uneven terrain between the two points, the mostly underground aqueduct followed a long, winding route that called for a bridge across the gorge of the Gardon River. 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, standing 48.8m high. The whole aqueduct descends in height by only 17 m over its entire length, while the bridge descends by a mere 2.5 centimetres which is indicative of the great precision that Roman engineers were able to achieve, using only simple technology. The aqueduct formerly carried an estimated 200,000 m3 of water a day to the fountains, baths and homes of the citizens of Nîmes. It continued to be used possibly until the 6th century, with some parts used for significantly longer, but lack of maintenance after the 4th century meant that it became increasingly clogged by mineral deposits and debris that eventually choked off the flow of water.
After the collapse of the Roman Empire and the aqueduct's fall into disuse, the Pont du Gard remained largely intact, due to the importance of its secondary function, as a toll bridge. For centuries the local lords and bishops were responsible for its upkeep, in exchange for the right to levy tolls on travellers using it to cross the river, although some of its stones were looted and serious damage was inflicted on it in the 17th century. It attracted increasing attention starting in the 18th century, and became an important tourist destination. It underwent a series of renovations between the 18th and 21st centuries, commissioned by the local authorities and the French state, that culminated in 2000 with the opening of a new visitor centre and the removal of traffic and buildings from the bridge and the area immediately around it. Today it is one of France's most popular tourist attractions, and has attracted the attention of a succession of literary and artistic visitors.References:
The city walls of Avila were built in the 11th century to protect the citizens from the Moors. They have been well maintained throughout the centuries and are now a major tourist attraction as well as a UNESCO World Heritage Site. Visitors can walk around about half of the length of the walls.
The layout of the city is an even quadrilateral with a perimeter of 2,516 m. Its walls, which consist in part of stones already used in earlier constructions, have an average thickness of 3 m. Access to the city is afforded by nine gates of different periods; twin 20 m high towers, linked by a semi-circular arch, flank the oldest ones, Puerta de San Vicente and Puerta del Alcázar.