Italy is a long, rocky peninsula, surrounded in the west by the Tyrrhenian Sea and east by the Adriatic Sea. It borders France, Switzerland, Austria and Slovenia in the north. The Alps formed the spine of this peninsula; and also the northern border. The northernmost lake with the largest lake is Garda (143 square miles; 370 square kilometers); Po, the main river, flows from the Alps on the western Italian border through the Lombardy Plain into the Adriatic Sea. Italy also owns several islands; The largest islands are Sicily (9,926 square miles; 25,708 square kilometers) and Sardinia (9,301 square miles; 24,090 square kilometers).