TIVOLI (anc. Tibur, q.v.), a town and episcopal see of the province of Rome, Italy, 18 m. E.N.E. of Rome by road and tramway, 241/2 m. by rail, 760 ft. above sea-level. Pop. (1901), 11,610 (town), 12,881 (commune). Tivoli lies on the west of the Sabine Mountains, where the river Anio issues from them, upon a limestone rock above the river. The town on one side overlooks the Campagna di Roma and Rome itself, on the other the deep gorge of the Anio, with its lofty falls, and the environs are very beautiful. The Roman remains are described under the heading of Tibur. The Villa d’Este, begun in 1549 by Pirro Ligorio for Cardinal Ippolito d’Este the younger (the cardinal of Ferrara), has the finest example of a Renaissance garden in Italy; it was erected on a steep slope, with many terraces, and embellished with numerous fountains, fantastically decorated in stucco, which once formed the background to the splendid collection of ancient statuary formed by the cardinal, but now dispersed (see F. S. Seni, La Villa d’Este in Tivoli, Rome, 1902; T. Ashby, in Archaeologia, vol. lxi.). The villa contains damaged frescoes by the brothers Zuccari. The register of the see of Tivoli has documents dating from the 10th century relating to the landed property of the see (L. Bruzza, Regesto della chiesa di Tivoli, Rome, 1883), and the municipal archives date from 1450. The castle was erected in 1460 by Pius II. on the site of the amphitheatre; it is now a prison. In November 1826 a flood of the Anio led to a change in its course, and threatened to carry away the town. A new channel, consisting of two parallel tunnels (the Traforo Gregoriano) 290 and 330 yds. long, was therefore made to the north-east in 1826–1835 by Folchi, and on emerging from these the river has a fall of 354 ft. Farther north-west are smaller falls (the cascatelle) of that portion of the river which is carried through the town and serves for industrial purposes. Five miles west are the sulphur baths of Acque Albule, which were known to the ancients, and are now frequented by over 40,000 persons annually. The temperature of the water is 75·2° F. The falls in the river afford electric power for lighting Rome and driving its trams, as well as for driving several factories in Tivoli itself. Tivoli is also the centre of an agricultural district, and its olive trees are especially fine.