Arnus

ARNUS(Ἄρνος: Arno), the principal river of Tuscany, and next to the Tiber the most considerable river of Central Italy. Strabo describes it as flowing from Arretium, and seems to have regarded it as rising near that city; but its real sources are nearly 30 miles further to the N., in one of the loftiest groups of the Tuscan Apennines, now called Monte Falterona, From thence it has a course nearly due S. till it approaches within a few miles of Arezzo(Arretium), when it turns abruptly to the NW., and pursues this direction for about 30 miles, as far as Pontassieve, where it again makes a sudden turn, and from thence holds its course nearly due W. to the Tyrrhenian Sea. In this latter part of its course it flowed under the walls of Florentia, and the more ancient city of Pisa; immediately below which it received, in ancient times, the waters of the Auser, or Serchio, which now pursue their own separate course to the sea. [AUSER] Strabo gives an exaggerated account of the violent agitation produced by the confluence of the two streams, which may, however, have been at times very considerable, when they were both swoln by floods. (Strab. 5. p. 222; Plin. Nat. 3.5. s. 8; Pseud. Arist. de Mirab. § 92; Rutil. Itin. 1.566.) Still more extraordinary is his statement that the stream of the Arnus was divided into three, the upper part of its course; though some writers have maintained that a part of its waters formerly turned off near Arretium, and flowed through the Val di Chianainto the Tiber. [CLANIS] Its mouth was distant, according to Strabo, only 20 stadia from Pisa; an estimate, probably, below the truth, but the coast line has certainly receded considerably, from the constant accumulation of sand. The present mouth of the Arno, which is above six miles below Pisa, is an artificial channel, cut at the beginning of the 17th century. (Targioni-Tozzetti, Viaggi in Toscana, vol. ii. pp.96, 97.) The whole length of its course is about 140 Italian, or 175 Roman, miles.
The Arnoreceives in its course numerous tributary streams, but of none of these have the ancient names been preserved to us. It has always been subject to violent floods, and inundates the fiat country on its banks throughout the lower part of its course. This must have been the case in ancient times to a still greater extent, and thus were formed the marshes through which Hannibal found so much difficulty in forcing his way on his march to Arretium. (Plb. 3.78, 79; Liv. 22.2, 3.) Strabo, indeed, supposes these marshes to have been on the N. side of the Apennines, and in the valley of the Padus (5. p. 217); but this seems to be certainly a mistake; Livy expressly refers them to the Arnus, and this position is at least equally consistent with the narrative of Polybius, who affords no distinct statement on the point. (Niebuhr, Lect. on Rom. Hist. vol. 1. p. 181; Vaudoncourt, Hist. des Campaynes d'Annibal, vol. i. pp. 136,156.) The marshy lakes, called the Paduli di Fucecchioand di Bientina, still existing between the Apennines and the N. bank of the Arno, are evidently the remains of a state of things formerly much more extensively developed. At a still earlier period it is probable that the basin or valley at the foot of the hill of Faesulae, in the centre of which now stands the city of Florence, was likewise a marsh, and that the narrow rocky gorge through which the river now escapes (just below the village of Signa, 10 miles from Florence) was formed, or at least widened, by artificial means. (Niebuhr, Vorträge ub. Völker u. Länder, p. 339.)
[E.H.B]