The Aqua Anio Vetus was an ancient Roman aqueduct, and the second oldest after the Aqua Appia. It was commissioned in 272 BC and funded by treasures seized after the victory against Pyrrhus of Epirus. Two magistrates were appointed by the Senate, the censors Manius Curius Dentatus (who died five days after the assignment) and Flavius Flaccus.
The aqueduct took water from the Anio river and acquired the nickname of Vetus ("old") only after the Anio Novus was built almost three centuries later..: §13
The Anio Vetus was an engineering masterpiece, especially considering its early date and complexity of construction. It was four times as long as the Aqua Appia and its source much higher. Its flow was more than twice that of the Aqua Appia: §6-20 and supplied water to higher elevations of the city. However, the Anio Vetus had muddy and discoloured water: §15 and probably did not supply drinking water to the Roman aristocracy.
Its source is believed to be between Vicovaro and Mandela, 850 m (2,790 ft) upstream of the gorge at San Cosimato. Like the Aqua Appia, its route was mainly underground.
It descended from its source along the valley to Tivoli, where it left the Anio towards the Alban Hills to near Gallicano, below Palestrina. It crossed under the Via Latina near the seventh milestone and at the fourth milestone turned northwest to enter Rome.
It entered the city underground at the Porta Praenestina and terminated inside the Porta Esquilina. Only 5.8% of the Vetus' total flow supplied imperial buildings,: §6–20 an important difference from the Appia, which provided almost 22% to such buildings.
It had 35 castella for distribution in the city.: §80
Three major restorations were done along with the Appia aqueduct: in 144 BC by the praetor Quintus Marcius Rex during construction of the Aqua Marcia, by adding a secondary conduit in the Casal Morena area; in 33 BC when Agrippa took control of the entire water system of the city; and between 11 and 4 BC by Augustus. With this latter, an underground branch was built, the specus Octavianus, that started from the current Pigneto area and followed the Via Casilina and reached the area where the Baths of Caracalla were later built.
Other restorations in the first two centuries AD include the construction of bridges across valleys on the route to shortcut long underground diversions. These include Ponte Della Mola, which dates to Hadrian and was built to cross a valley shortening the route by about 1.5 km (0.93 mi). It is 156 m (512 ft) long and 24.5 m (80 ft) high with a double order of 29 arches and two single arches. The central part, for a stretch of three double arches, collapsed in 1965 and an adjacent fourth double arch was soon demolished because it was unsafe.
Remains of the bridges Ponte Taulella, Ponte Pischero, Ponte degli Arci, and Ponte Lupo still exist.