The Po is the longest river in Italy. It is a river that flows eastward across northern Italy starting from the Cottian Alps. The Po flows either 652 km (405 mi) or 682 km (424 mi) – considering the length of the Maira, a right bank tributary. The headwaters of the Po are a spring seeping from a stony hillside at Pian del Re, a flat place at the head of the Val Po under the northwest face of Monviso. The Po then extends along the 45th parallel north before ending at a delta projecting into the Adriatic Sea near Venice.