1911 Encyclopædia Britannica/Tiber

TIBER (anc. Tiberis; Ital. Tevere), a river of central Italy. It traverses the Tuscan Apennines—in which it rises at a point some 12 m. N. of Pieve San Stefano, 4160 ft. above sea-level —in a series of picturesque ravines, 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 104 m., though, owing to the rapidity of the current, there is very little navigation above Rome. The total length of the river is 240 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 180 tons burden and proposals have been made to embank and dredge it so as to increase this depth to 8 ft. at least, or to build a ship canal up to Rome. The area of the Tiber basin is 6845 sq. m. The stream is heavily charged with sediment, and from that circumstance got its ancient epithet of flavus (tawny). It does not, however, form a delta proportionate to the volume of its water, owing to a strong sea current flowing northwards close to the shore, to the sudden sinking of the sea to a great depth immediately off the mouth of the river, and possibly also to the permanent subsidence of the Italian coast from the Tiber mouth southwards to Terracina. Still it has advanced at each mouth about 2 m. since Roman times, while the effect of the sediment 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 6.5.: 1000. The arm which reaches the sea at Fiumicino is a canal, dug by Claudius and improved by Trajan (see Portus), which partially silted up in the middle ages, and was reopened for navigation by Paul V. in 1612, 2 1/2 m. long, 80–130 ft. wide, and with a minimum depth of 5 ft. The lower course of the Tiber has been from the earliest ages subject to frequent and severe inundations; of more recent ones, those of 1598, 1870 and 1900 have been especially destructive, but since the year 1876 the municipality of Rome, assisted by the Italian Government, has taken steps to check, and possibly to prevent these calamities within the city by constructing embankments of stone, resting on caissons, for a total distance (counting in both sides of the river) of 6 miles. The flood of 1900 carried away about 1/4 m. of the new embankment on the right bank of the right arm opposite the island owing to the faulty planning of the course of the river at that point, which threw the whole of the water into the right arm, and except in flood time, left the left arm dry—a fault which has since been corrected.

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). The flood of 1900, when the river both above and below Rome extended over the whole width of its valley, from hill to hill, and over most of the low ground at its mouth, gave an idea of the conditions which must have existed in prehistoric days.