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Last edited 18 Sep 2020
An aqueduct is a channel that has been constructed for the specific purpose of carrying water from one point to another. The source and distribution point may be a significant distance apart, and the water is often transported over an elevated masonry or brick structure - often in the form of a bridge - supported on arches. It can also be carried through a series of tunnels or other underground systems.
Before being adopted by engineers of the Roman empire, this ancient water delivery system had already appeared on a small scale in many different parts of the world including Greece, Egypt, Jordan, Persia, Oman, India and the Americas. These aqueducts were primarily used to supply irrigation systems for farming purposes, but the waterways also provided bathing and drinking water to some parts of the population.
Some of the earliest Roman aqueducts date back to the fourth century BC. The first of these structures, the Aqua Appia, was used to supply water from approximately 10 miles outside of the city. This aqueduct was mostly underground until it reached the edge of the city. At this point, it emptied into a series of reservoirs that distributed water to different parts of the city.
The need for fresh water drove the construction of complex aqueducts. These used the basic properties of gravity and the construction of a series of channels that gradually declined over significant distances (sometimes of 50 miles or more). A steeper gradient allows a smaller channel to carry the same amount of water as a larger channel with a lower gradient, but it must start from a higher point to reach the same distance.
 Increasing popularity and sophistication
As the empire grew, so did the sophisticated network of aqueducts along with the construction, maintenance and inspection practices that protected them. Many aqueducts included purification systems in the form of sedimentation tanks. Distribution tanks would control the flow of the water to different locations.
The Roman network of aqueducts became an essential part of the empire’s urban planning initiatives.
|Despite being partially destroyed by the Moors in 1072, the Aqueduct of Segovia is one of the best-preserved elevated Roman aqueducts.|
In Segovia, Spain, the Aqueduct of Segovia is a testament to the importance of good construction and maintenance. At one time the Romans employed more than 700 people just to maintain their aqueduct network.
In France, the Pont du Gard, near Nimes, survives as an example of Roman engineering skill. Each large arch spans approximately 25 metres (82 feet) and is constructed of un-cemented blocks weighing nearly two tons. The small top arches, which carry the channel, were placed in groups of three over the larger arches below.
|The finished Pont du Gard aqueduct transported water to Nimes over a distance of 30 miles and provided each resident of the ancient city with about 380 litres (100 gallons) of water per day.|
The remains of other ancient aqueducts still stand in many Roman cities, both in Italy and other parts of the former empire. Some have been maintained and are still partially in use, although most fell into disrepair, and some were intentionally destroyed by the enemies of Rome as a tactical measure.
Complex aqueduct systems of this type have been used to transport water in California, Arizona, New York State and other places throughout the United States. An aqueduct system in China (the South-North Water Transfer Project) will eventually direct water from the Yangtze River to Beijing.
 Aqueducts of the world
The following list provides an overview of some of the dates and locations of noteworthy aqueducts around the world.
- Mosul (formerly Nineveh), Iraq, Jerwan aqueduct (688 BC)
- Samos, Greece, Eupalinian aqueduct (built sometime from 538 to 522 BC)
- Nimes, France, Pont du Gard (built in the 1st century AD)
- Segovia, Spain, Aqueduct of Segovia (construction dates unknown, but roughly 1st century AD)
- Istanbul, Turkey, Valens aqueduct (4th century AD)
- Acambaro, Mexico, Acambaro aqueduct (1528)
- Bar, Montenegro, Bar aqueduct (16th century)
- Rio de Janeiro, Brazil, Carioca aqueduct (1744-1750)
- New York State water supply system aqueducts for New York City (1837 through 1945)
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