Almost 40% of the Italian territory is mountainous,[1] with the Alps as the northern boundary and the Apennine Mountains forming the backbone of the peninsula and extending for 1,350 km (840 mi).[1] In between the two lies a large plain in the valley of the Po, the largest river in Italy, which flows 652 km (405 mi) eastward from the Cottian Alps to the Adriatic. The Po Valley is the largest plain in Italy, with 46,000 km2 (18,000 sq mi), and it represents over 70% of the total plain area in the country.[1]