The Aqua Claudia on the Palatine Hill in Rome, June 2012

Aqua Claudia was an aqueduct of ancient Rome that, like the Anio Novus, was begun by Emperor Caligula in 38 AD. and finished by Emperor Claudius in 52 AD. Its main springs, the Caeruleus and Curtius, were situated 300 paces to the left of the thirty-eighth milestone of the Via Sublacensis. After being in use for ten years, the supply failed, and was interrupted for nine years, until Emperor Vespasian restored it in 71, and ten years later Titus once more.

The channel length was 45–46 miles (ca. 69 km, most of which was underground), and volume at the springs was 191,190 cubic metres in 24 hours. Following Nero's completion of the Arcus Neroniani, one of the aqueduct's branches, the Aqua Claudia could provide all 14 Roman districts with water. Directly after its filtering tank, near the seventh mile of the Via Latina, it finally emerged onto arches, which increase in height as the ground falls towards the city. It is also one of the two ancient aqueducts that flowed through the Porta Maggiore, the other being the Anio Novus. It is described in some detail by Frontinus in his work published in the later first century, De aquaeductu. The church of San Tommaso in Formis was later built into the side of the acqueduct.

Text from: en.wikipedia.org/wiki/Aqua_Claudia