TIBER, a river of central Italy (anc. Tiberis; Ital. Tevere). It traverses the Tuscan Apennines—in which it rises at a point some 12 m. N. of Pieve San Stefano, 4,160 ft. above sea-level, nearly 20 m. east from the headwaters of the Arno--in a series of picturesque ravines, flows nearly south by Borgo S. Sepolcro and Cita di Castello, then runs between Perugia and Todi to Orte, where it receives the Nera (which brings with it the waters of the Velino; see TERNI), skirts the west foot of the Sabine Mountains in a broad shallow valley, then crosses the Roman Campagna, cutting its way through Rome, and finally enters the Tyrrhenian (Mediterranean) Sea by two arms at Ostia and Fiumicino, the latter artificial. Its principal tributaries are the Paglia, the Nera and the Anio or Teverone, and it is generally navigable by boats up to the confluence of the Nera, a distance of 1o4 m., though, owing to the rapidity of the current, there is very little navigation above Rome. The total length of the river is 253 m., of which 21 m. lie between Rome and the sea. This latter portion of the river's course is tortuous, but in spite of this, and although the depth varies from only 7 to 20 ft., and in places at low water does not exceed 4 ft., it is nevertheless navigated by vessels up to 18o tons burden. The area of the Tiber basin is 6,719 sq.m., and it is the largest in Italy except the Po. The
stream is heavily charged with sediment, and from that circum stance got its ancient epithet of flavus (tawny). The discharge at the mouth is 23o cubic metres per second, but it can fall as low as 90, and in floods rise to 3,400. It has advanced at each mouth about 2 m. since Roman times, while the effect of the sedi ment it brings down is seen on the north-west almost as far as Palo (anc. Alsium), and on the south-east beyond Tor Paterno (see LAURENTINA, VIA) in the gradual advance of the coast. The rate of advance at Fiumicino is estimated at 13 ft. per annum. From Rome to the sea the fall is only 6: i,000. The arm which reaches the sea at Fiumicino is a canal, dug by Claudius and im proved by Trajan (see PoRTus).
In the prehistoric period the mouth of the Tiber must have been situated at the point where the hills which follow it on each side cease, about 12 m. below Rome. On the right bank they are of Pliocene gravel, on the left of tufa; and on the latter, on a cliff above the river (the ancient Puilia saxa) stood Ficana (marked by the farmhouse of Dragoncello), which is said to have owed its origin to Ancus Martius. Beyond these hills the low coast belt formed by the solid matter brought down by the river begins; and on each side of the mouth in the flat ground were salt marshes. (See OSTIA, PORTUS.)