Another lateral rsnge, the Prato Magno, which branches off from the central chain at the Monte Falterona, and separates the upper valley of the Arno from its second basin, rises to 5188 ft.; while a similar branch, called the Alpe di Catenaja, of inferior elevation, divides the upper course of the Arno from that of the Tiber.
The Serchio (anc. Auser), which joined the Arno at Pisa in ancient times, now flows into the sea independently.
It is a singular fact in the geography of Central Italy that the valleys of the Tiber and Arno are in some measure connected by that of the Chiana, a level and marshy tract, the waters from which flow partly into the Arno and partly into the Tiber.
The Arno is navigable for barges as far as Florence; but it is liable to sudden floods, and brings down with it large quantities of earth and stones, so that it requires careful regulation.
A conception of the size of the whole necropolis may be gathered from the fact that nearly three thousand Etruscan inscriptions have come to light from Clusium and its district alone, while the part of Etruria north of it as far as the Arno has produced barely five hundred.
The Elsa and the Era, which join it on its left bank, descending from the hills near Siena and Volterra, are inconsiderable streams; and the Serchio, which flows from the territory of Lucca and the Alpi Apuani, and formerly joined the Arno a few miles from its mouth, now enters the sea by a separate channel.
The most considerable rivers of Tuscany south of the Arno are the Cecina, which flows through the plain below Volterra, and the Ombrone, which rises in the hills near Siena, and enters the sea about 12 m.
Coast of the Crimea, where a climate similar to that of the Mediterranean coast has permitted the development of a flora closely resembling that of the valley of the Arno in Italy.