Aqueduct (bridge) in the context of "Viaduct"

A bridge is a structure that crosses an obstacle such as a river, lake, railroad, road, or ravine. Its primary function is to transport vehicles, trains, and pedestrians, but bridges may also accommodate pipelines, buildings, wildlife, and canals. Basic structures used in bridge design include arches, trusses, beams, cantilevers, suspension cables, and cable-stays. Bridges are configured in a variety of forms, such as viaducts, aqueducts, trestles, movable bridges, double-deckers, pontoons, and portable military bridges. They may also be categorized by their materials, which include wood, brick, stone, iron, steel, and concrete.

The history of bridges reflects the evolution of humankind's engineering technologies. The Romans and ancient Chinese built major bridges of stone and timber. During the Renaissance, advances in science and engineering led to wider bridge spans and more elegant designs. Concrete was perfected in the early 1800s, and proved to be superior to stone in many regards. With the Industrial Revolution came mass-produced steel, which enabled the creation of suspension and cable-stayed bridges that could span wide obstacles.

An aqueduct is a watercourse constructed to carry water from a source to a distribution point far away. In modern engineering, the term aqueduct is used for any system of pipes, ditches, canals, tunnels, and other structures used for this purpose. The term aqueduct also often refers specifically to a bridge carrying an artificial watercourse.

Aqueducts were used in ancient Greece, the ancient Near East, ancient Rome, ancient Aztec, and ancient Inca. The simplest aqueducts are small ditches cut into the earth. Much larger channels may be used in modern aqueducts. Aqueducts sometimes run for some or all of their path through tunnels constructed underground. Modern aqueducts may also use pipelines. Historically, agricultural societies have constructed aqueducts to irrigate crops and supply large cities with drinking water.

The Romans constructed aqueducts throughout their Republic and later Empire, to bring water from outside sources into cities and towns. Aqueduct water supplied public baths, latrines, fountains, and private households; it also supported mining operations, milling, farms, and gardens.

Aqueducts moved water through gravity alone, along a slight overall downward gradient within conduits of stone, brick, concrete or lead; the steeper the gradient, the faster the flow. Most conduits were buried beneath the ground and followed the contours of the terrain; obstructing peaks were circumvented or, less often, tunneled through. Where valleys or lowlands intervened, the conduit was carried on bridgework, or its contents fed into high-pressure lead, ceramic, or stone pipes and siphoned across. Most aqueduct systems included sedimentation tanks, which helped to reduce any water-borne debris. Sluices, castella aquae (distribution tanks) and stopcocks regulated the supply to individual destinations, and fresh overflow water could be temporarily stored in cisterns.

The Pont du Gard is an ancient Roman aqueduct bridge built in the first century AD to carry water over 50 km (31 mi) to the Roman colony of Nemausus (Nîmes). It crosses the river Gardon near the town of Vers-Pont-du-Gard in southern France. The Pont du Gard is one of the best preserved Roman aqueduct bridges. It was added to UNESCO's list of World Heritage sites in 1985 because of its exceptional preservation, historical importance, and architectural ingenuity.

The Aqueduct of Segovia (Spanish: Acueducto de Segovia) is a Roman aqueduct in Spain, built around the first century AD to channel water from springs in the mountains 17 kilometres (11 mi) to Segovia's fountains, public baths and private houses, in use until 1973. Its elevated section, with its complete arcade of 167 arches, is one of the best-preserved Roman aqueduct bridges and the foremost symbol of Segovia, as evidenced by its presence on the city's coat of arms. The Old Town of Segovia and the aqueduct were declared a UNESCO World Heritage Site in 1985.