major tributary of the Tiber (Tevere) River in central Italy. It rises from two springs in the Simbruini Mountains near Subiaco, southeast of Rome, flows through a narrow valley past Tivoli, and meanders through the Campagna di Roma (territory) to join the Tiber north of Rome. It is 67 miles (108 km) long and has a drainage basin of 569 square miles (1,474 square km). The Roman emperor Nero created a group of artificial lakes in the upper course of the river above Subiaco and built a villa there, the remains of which survive. In Roman times, two huge aqueducts, the Anio Vetus and the Anio Novus, supplied Rome with water from the river. The series of falls at Tivoli, where the Aniene descends from the mountains to the plain, were once a main scenic attraction of the Roman countryside; but the heavy use of the river's waters by hydroelectric plants and by aqueducts has reduced the once-famous cascades to a trickle.