Tivoli (anc. Tibur), a town of Italy, in the province and 16 m. E. N. E. of the city of Rome, on the Teverone (anc. Anlo) and on the slope of Mt. Ripoli; pop. about 6,000. It is remarkable for magnificent scenery and for its antiquities, which include villas, bridges, and the temples of the Sibyl and of Vesta. The celebrated falls of the Anio were best seen from the grottoes of Neptune and the Sirens till 1820, when the artificial wall over which they flowed was destroyed by an inundation. The course of the river was then diverted by cutting two long tunnels through the rock of Mt. Catillo, finished in 1834; the new falls thus formed are exceedingly picturesque, as well as the numerous small cascades in the TV. part of the town. - The ancient Tibur, probably a Siculian city, was one of the early rivals of Rome. As a member of the Latin league, it was, after a protracted struggle, taken in 338 13. C, and deprived of a part of its territory. Remaining nominally independent, it became a resort of Roman exiles. It was famed for the worship of Hercules in one of the most beautiful temples of the period, and for its associations with illustrious Romans who had villas here during the republic and the early days of the empire.

The domain of Hadrian, S. of Tibur, extended over 8 m., and included many public buildings besides a magnificent palace. In the middle ages the town again became important. Pius II. built the castle in its present form near the gate Santa Croce.