ĂQUAE DUCTUS (ὑδραγωγία), literally, a water-conduit, but the word is used especially for the magnificent structures by means of which Rome and other cities of the Roman empire were supplied with water. A Roman aqueduct, often called simply _aqua_, may be described in general terms as a channel, constructed as nearly as possible with a regular declivity from the source whence the water was derived to the place where it was delivered, carried through hills by means of tunnels, and over valleys upon a substruction of solid masonry or arches. The aqueduct is mentioned by Strabo as among the structures which were neglected by the Greeks, and first brought into use by the Romans. Springs (κρῆναι, κρουνοί) were sufficiently abundant in Greece to supply the great cities with water; and they were frequently converted into public fountains by the formation of a head for their waters, and the erection of an ornamental superstructure. Of this we have an example in the _Enneacrunos_ at Athens, which was constructed by Peisistratus and his sons. The Romans were in a very different position, with respect to the supply of water, from most of the Greek cities. They, at first, had recourse to the Tiber, and to wells sunk in the city; but the water obtained from those sources was very unwholesome, and must soon have proved insufficient, from the growth of the population. It was this necessity that led to the invention of aqueducts, in order to bring pure water from the hills which surround the Campagna. The number of aqueducts was gradually increased, partly at the public expense, and partly by the munificence of individuals, till, in the fourth century of the Christian era, they amounted to fourteen. Of these only four belong to the time of the republic, while five were built in the reigns of Augustus and Claudius.--1. The _Aqua Appia_, begun by the censor Appius Claudius Caecus in B.C. 313. Its sources were near the _Via Praenestina_, between the seventh and eighth mile-stones.--2. The _Anio Vetus_ was commenced forty years later, B.C. 273, by the censor M. Curius Dentatus, and was finished by M. Fulvius Flaccus. The water was derived from the river Anio, above Tibur, at a distance of 20 Roman miles from the city; but, on account of its windings, its actual length was 43 miles.--3. The _Aqua Marcia_, one of the most important of the whole, was built by the praetor Q. Marcius Rex, by command of the senate, in B.C. 144. It commenced at the side of the _Via Valeria_, 36 miles from Rome.--4. The _Aqua Tepula_, built by the censors Cn. Servilius Caepio and L. Cassius Longinus in B.C. 127, began at a spot in the Lucullan or Tusculan land, two miles to the right of the tenth milestone on the _Via Latina_. It was afterwards connected with.--5. The _Aqua Julia_, built by Agrippa in his aedileship, B.C. 33. It was conducted from a source two miles to the right of the twelfth milestone on the _Via Latina_, first to