High Quality Content by WIKIPEDIA articles! The Winter Line was a series of German military fortifications in Italy, constructed during World War II by Organisation Todt. The primary Gustav Line ran across Italy from just north of where the Garigliano River flows into the Tyrrhenian Sea in the west, through the Apennine Mountains to the mouth of the Sangro River on the Adriatic coast in the east. The centre of the line, where it crossed the main route north to Rome (Highway 6) which followed the Liri Valley, was anchored around the mountains behind the town of Cassino including Monte Cassino, on which was situated an old abbey that dominated the entrance to the Liri Valley (a main route to Rome), and Monte Cairo which gave the defenders clear observation of potential attackers advancing towards the mouth of the Liri valley.