The term 'SOURCE OF THE PO' is solved by the crossword answer ALPS, which stands for the ALPS mountain range. The ALPS are a large mountain range located in Europe, stretching from Austria and Slovenia in the east, through Italy, Switzerland, Liechtenstein and Germany to France in the west. The source of the Po River, the longest river in Italy, is located in the ALPS. The Po River begins at an elevation of 2, 400 meters in the Monte Viso massif of the ALPS and flows through northern Italy before emptying into the Adriatic Sea.