PNYX, niks, in ancient Greece, a hill in Athens where the people assembled to make de crees, pass laws, etc.
PO, pi (ancient PADUS, or ERIDANUS ) , the largest• river of Italy, in respect both of its length and its volume of water. It rises on the confines of France and Piedmont in Mount Viso, one of the Cottian Alps, and flows rapidly eastward through Piedmont in the character of a mountain torrent, till, after having been aug mented by several other mountain streams, it reaches Lombriasco. Here it begins to move more slowly and after passing Turin, becomes somewhat sluggish. It again flows eastward to the Adriatic Sea. It is about 400 miles long, and its drainage basin covers the larger part of northern Italy. In its lower course its banks are protected by levees and dikes, as the sur face of the river is higher than the surrounding country. A number of rivers, chiefly from the Alps, flow into the Po. Its principal affluents are, on the left, the Clusone, Sangone, Dora Riparia, Stura, Dora-Baltea, Sesia, Agogna, Terdoppio, Ticino or Tessin, Olona, Lambro, Adda, Oglio and Mincio; on the right, the Vraita, Tanaro, Scrivia, Trebbia, Nura, Taro, Parma, Enza, Secchia and Panaro. It drains the famous Lake Como, also Maggiore, Iseo and Garda. Pavia, Milan, Mantua, Parma and
Modena are all located in its tributaries. After receiving the Adda its average breadth is about 650 yards. Below Piacenza, which it passes on the right, it is confined by artificial embankments, which are said to have originated with the ancient Etruscans, and notwithstanding the immense sums which have been expended upon them, and the engineering skill which has been exerted in order to render them perfectly secure, the most disastrous inundations have repeatedly taken place. The embankments themselves have added to the danger. The deposits made by the river are perpetually tend ing to raise the level of the water. This makes it necessary to make a corresponding increase in the height of the embankment, and the effect of these combined operations has been to lift the river so high above its natural bed that it is actually on a level with the tops of the houses in the city of Ferrara. The Po is well supplied with fish, including, among others, the shad, salmon and sturgeon. The deposits brought from the mountains are increasing the extent of the delta, which advances into the Adriatic at the rate of 200 feet each year.