AQUEDUCT. Sennacherib of Nineveh seems to have been the first to build an aqueduct. He carried a great irrigation canal across a tributary of the Atrush-Gomel, near modern Jerwan, on a ninety ft. bridge of five pointed arches over thirty ft. high. It was built of twenty-inch cubes of stone with a channel sealed by mortar. Hezekiah’s Siloam tunnel was an aqueduct which showed a similar standard of engineering. Polycrates of Samos and the 2nd cent. b.c. engineers of Hel. Pergamum also built efficient aqueducts, but of all ancient peoples the Romans produced the greatest hydraulic engineers and the finest aqueducts.

Remains of these great waterworks are to be found in all parts of the old domains of the empire. The Rom. aqueduct bridges were built on a simple pattern. On a row of tall piers of stone or brick rose a series of small round arches. Above these lay the water channel of concrete, with an arched roof above it. Where the conduit crossed a deep depression, as at Segovia, Tarragona, or Smyrna, two or three rows of arches were superimposed. The famous Pont du Gard at Nimes (ancient Nemausus) has three such arcades. These arcades or bridges were, of course, only part of the total system. They were conspicuous and have tended to survive, but tunnels and channels carried the water over most of its course. Only thirty m. of Rome’s 260 m. of aqueducts which functioned in the first cent. were thus elevated. The rest ran in low conduits or underground. Nearly all of the Aqua Appia, the first of Rome’s aqueducts, built by Appius Claudius Caecus, builder of the Appian Way, was subterranean. It was begun in 312 b.c. and carried the water of the Anio ten m. into Rome.

Estimates of the volume of water delivered by aqueduct into imperial Rome vary, but a reasonable figure would be 200,000,000 gallons a day, a generous supply for 1,000,000 inhabitants. Costs were high, as an estimate of Pliny, governor of Bithynia in a.d. 112, shows. Pliny reported to Trajan (Ep. 10.37) that the city of Nicomedia, after spending “an immense sum” on an aqueduct, had been forced to abandon the work. Pliny suggested a reasonable alternative, efficient and soundly financed. In Pal. may be seen a considerable section of aqueduct used to supply Caesarea with water, and a few traces of the aqueduct which Pilate built in Jerusalem are left. He financed the scheme from the Corban fund and clashed seriously with the Jewish authorities (Jos. War II. ix. 4).

Bibliography L. S. De Camp, The Ancient Engineers (1963).