The valley of the Aniene (Anio) is crossed by two great aqueducts that carried water to Rome. In San Gregorio da Sassola passes the Anio Vetus (Old), the first to be produced, the path of which is mainly in a channel or underground. In the stretch crossing the valley of the Fosso della Mola, to maintain the correct slopes, the Romans built a massive bridge that does not date back to the original aqueduct but was built later by Hadrian’s engineers.
The Anio Vetus was the second aqueduct built for Rome and was built 272-269 BC from the proceeds of the victory over Pyrrhus. It was 63 Km long, passed through Porta Maggiore and ended at Esquilino.
The water quality was often cloudy and in imperial times it was used to power of ornamental fountains and irrigation. The estimated capacity was more than 2000 liters per second, in Rome about half the capacity due to leaks and illegal connections