Aqueducts are structures used to carry water from a supply source to distant areas in need of water. The word aqueduct comes from two Latin words, aqua (water) and ducere (to lead). The first aqueducts were built as early as the tenth century B.C. by ancient communities. While primitive people lived very close to water, as people moved inland and away from direct water supplies, they created systems of water retrieval. Wells were dug to reach underground water supplies. Also, cisterns, underground collecting tanks, were used to store water. Eventually, dams were constructed to block water flow, allowing water pressure to increase, and run-off channels were constructed to guide water to specific regions. Early aqueducts redirected water by use of conduits (covered canals, or pipes, usually made of stone) that were often buried a few inches below ground for protection. Aqueducts were driven by the force of gravity pulling water downhill and extended for many miles. The use of aqueducts for drinking water, agriculture, and other uses is a part of Greek, Mexican, Roman, and Asian history. The city of ancient Rome had 11 active aqueducts traversing roughly 300 mi (485 km). Modern aqueducts use electrical power to elevate water that travels through many miles of pipes. Many modern pipes are deep beneath the ground and supply cities with water for personal and industrial use.