the largest river in Italy, called by the ancients Padus or Eridanus, rises on the E. side of Monte Viso, one of the highest summits of the Alps, between Italy and France; N. Lat. 44° 40', E. Long. 7°. At first a mere mountain torrent, it flows eastward down the deep Val d'Oro; and being augmented by other streams like itself, turns to the left, and sweeps round the northern edge of the Monferrato hills. After describing nearly a semicircle, it emerges at Valenza into the broad plain of Lombardy, through which it flows eastward to the Adriatic, fed by the rivers that flow on the one side from the Alps and on the other from the Apennines. Its great volume, supplied from the everlasting snows of the Alps, renders the country liable to those destructive floods which have furnished the Latin poets with some of their finest comparisons. From Piacenza downwards, the river is confined by artificial embankments of very ancient origin; but these do not always prevent the danger. The constant deposits of soil tend to raise the bed of the stream above the surrounding country, so that at Ferrara the Po is on a level with the tops of the houses. For the last 200 miles of its course the breadth of the river varies from 400 to 600 yards, and the depth from 2 to 6 fathoms. Near its mouth it divides itself into two arms, each falling into the sea by several mouths, one belonging to each arm being accessible to small ships. Formerly the Po followed a different course to the sea, south of Ferrara, and its old channel is now filled partly by canals from the main river, and partly by the Reno from the Apennines. Considerable changes seem to have taken place on the coast-line, from the gradual deposit of sand and mud by the river; and indeed the whole lower part of the Lombard plain seems to have been gradually formed in this way. But these processes must have been accomplished for the most part ages before the historic period.

The whole length of the Po is estimated at 420 miles; and it is navigable for barges and river steamers to a distance of 60 miles from its source. The upper part of its course lies entirely in the Sardinian territories; but after its confluence with the Ticino it separates Austrian Italy from the duchies of Parma and Modena on the north, and from the Papal States on the south. The principal affluents of the Po are,—on the north, the Dora Baltea from Mont Blanc, the Sesia from Monte Rosa, the Ticino from lake Maggiore, the Adda from the lake of Como, and the Mincio from the lake of Garda; and on the south, the Tanaro in Piedmont, the Trebbia and Taro in Parma, and the Secchia in Modena. The Po abounds in fish of various kinds, especially shad, salmon, and sturgeon. It imparts great fertility to the adjacent country. The free navigation of the Po is secured by a treaty concluded between Austria, Parma, and Modena in July 1850.