ANIO, a river of Italy about 75 miles long; the principal trib utary of the Tiber in its lower course. It rises in the limestone mountains east of Subiaco, and thence to Tivoli the road follows its narrow valley. The water of the river supplied Rome in ancient times (see AQUEDUCT), while the pure and copious springs which served for the ancient Aqua Marcia and Aqua Claudia, and still form the city's main supply, are in its valley. But the praeceps (hurrying) Anio of Horace has been transformed by hydro-electric power-plants for the supply of Rome, and the famous waterfalls at Tivoli (q.v.) will be largely curtailed. From Tivoli to its junction with the Tiber it pursues a winding course through the low ground, and formed an effective protection to Latium from the north.
See Colasanti, L'Aniene (well illustrated, Bergamo, 1906).