Aqueduct (Lat. aquœ, of water, and ductus, a channel; formerly spelled aquœduct), a channel for the conveyance of water, or, in the more general acceptation of the word, a structure raised above the surface, upon which water conduits are laid. Methods of supplying water which do not include such structures are commonly called water works. The use of these conveyances for water to supply cities may be traced back to a very remote period in Persia and in Judea. The "pools of Solomon," near Bethlehem, were three large reservoirs connected with each other, from which water was conveyed to Jerusalem, 6 m. distant. One of these pools was 582 ft. long, and, at an average, about 180 wide. Jerusalem is still supplied with water from them through a 10-inch earthen pipe. In Egypt and Babylonia similar works were constructed in very early ages. Enough remains of the ancient aqueduct of Carthage to show that it was one of the most remarkable of these great works; upon it the waters from the mountains of Zeugis were conveyed through an arched conduit 6 ft. wide and 4 ft. deep. The whole length was 70 m. The ruin here illustrated is that of an arcade near Undena, composed of 1,000 arches, many of which were over 100 ft. in height.

In its construction hydraulic cement was largely used, which is at present so solid that a single piece over 100 feet in length has fallen from the top without being broken. The ancient city of Mexico was supplied with water by the aqueduct of Chapultepec, built by Montezuma, and carried across the lake upon a causeway. But no aqueducts, ancient or modern, equal in length or in expense of labor those constructed by the incas of Peru. To irrigate their sterile soil, they brought water from the reservoirs of the mountains several hundred miles off. The aqueducts passed along the precipitous sides of the Andes, penetrating some by tunnels worked through the solid rock without iron tools, and crossing chasms upon walls and arches of solid masonry. The conduit was constructed of large slabs of freestone, which were closely fitted together without cement. The works have long since fallen to ruins. - The Romans, however, exceeded all other nations, ancient and modern, in the construction of these works. A treatise De Aquœductibus Urbis Romœ was written by the consul Sextus Julius Frontinus, who had the direction of the aqueducts under the emperor Nerva. He refers to nine different aqueducts, which brought into the city daily 28,000,000 cubic-feet of pure water.

The number of these was afterward increased to 24, some of which had several channels placed one above another, and extending many miles. They were built on a grade of regular descent, winding around the hills or penetrating them by tunnels, and in the low levels supported on arches, which sometimes, as in the New Anio, extended for 6 1/2 m. in one continued series, many of the arches more than 100 ft. high. The whole length of this aqueduct was over 63 miles. The Aqua Martia, which extended 38 miles, contained nearly 7,000 arches. The conduits were constructed in brick or in stonework laid in cement. There were numerous openings for ventilation and cisterns for collecting the sediment, in consequence of which the water was very pure. The Aqua Julia and Aqua Tepula were conveyed into the city upon the same structure, though at a higher level. The Aqua Claudia took its rise 38 m. from Rome, and approached it by a circuitous route, being led under ground 36 1/2 m. and along 7 m. of cut stone arcades of sufficient height to supply the hills of Rome. The capacity of all the aqueducts was wonderful in proportion to the population.

Strabo said that whole rivers flowed through the streets of Rome. It is estimated that 50,000,000 cubic feet of water must have been supplied daily to a population of 1,000,000, or about 312 imperial gallons to each individual. This is about ten times the supply from the three aqueducts at present in use. The Romans built other aqueducts also in their provinces, some of which exceeded in grandeur those which supplied the capital. That of Metis (Metz) in Belgic Gaul is among the most remarkable. Extending across the valley of the Moselle, it conveyed the waters of the river Gorse to the city in such quantity that from it basins were filled in which mock naval engagements took place. The ruins of this great work still remain. There may also be cited the aqueducts of the island of Mitylene, of Antioch, of Segovia in Spain, and of Constantinople. The aqueduct of Antioch was supplied from Beit el-Ma, 6 m. distant. The illustration given is that of a portion of one of the main bridges, 700 ft. long and 200 ft. high. Though solidly built, it is vet the rudest example of Roman work, and contrasts strangely with the bridge of the aqueduct of Nimes, or Pont du Gard, across which the waters of the river Hurc were led.

This bridge spanned the valley of the river Gard by a triple row of arches, the first six having a span of 60 ft. each; above these were 12 i-ir ones; while the upper row was composed of 36 smaller arches arranged as in the illustration, the whole forming one of the finest examples of Roman architecture. In 1740 the engineer Pitot built a roadway beside this aqueduct and level with its lowest tier of arches. The aqueduct of Spoleto is of uncertain origin. One of the bridges is 810 ft. long, and the main arches are 240 ft. high. This work remains entire. Though the Romans constructed their aqueducts so as to obtain a gradual descent, it is evident that they were not compelled to do so from ignorance of other methods. Prof. Leslie obtained a lead pipe supposed to have been used at the baths of Caracalla; and Delorme states that the waters from Mount Pila crossed three valleys through inverted syphons. The water was collected in a reservoir upon one hill and conducted through nine lead pipes 8 1/2 in. in diameter and 1 1/12 in. thick down the hillside, thence along an arcade 80 ft. high, and up the opposite slope, where it was discharged into a second reservoir.