Conduit built to carry water from its source to a main distribution point. Ancient Rome's aqueduct system, an extraordinary feat of engineering, brought water to the city from as far as 57 mi (92 km) away. Only a portion of the Roman aqueducts utilized the familiar stone arch; most were underground conduits made of stone or terra-cotta pipe. Modern aqueduct systems employ cast iron or steel. See alsowater-supply system.