"spine" of Italy. On the western front, the American Fifth Army, commanded by Lieutenant General Mark W. Clark, which had suffered very heavy casualties during the main landing at Salerno (codenamed Operation Avalanche) in September, moved from the main base of Naples up the Italian "boot" and on the eastern front the British Eighth Army, commanded by General Sir Bernard Montgomery, advanced up the Adriatic coast. Clark's Fifth Army made slow progress in the face of difficult terrain, wet weather and skillful German defences. The Germans were fighting from a series of prepared positions in a manner designed to inflict maximum damage, then pulling back while buying time for the construction of the Winter Line defensive positions south of the Italian capital of Rome. The original estimates that Rome would fall by October 1943 proved far too optimistic. Although in the east the German defensive line had been breached on the Adriatic front and Ortona was captured by the 1st Canadian Division, the advance had ground to a halt with the onset of winter blizzards at the end of December, making close air support and movement in the jagged terrain impossible. The route to Rome from the east using Route 5 was thus excluded as a viable option leaving the routes from Naples to Rome, highways 6 and 7, as the only possibilities; Highway 7 (the old Roman Appian Way) followed along the west coast but south of Rome ran into the Pontine Marshes, which the Germans had flooded. Highway 6 ran through the Liri valley, dominated at its south entrance by the rugged mass of Monte Cassino above the town of Cassino. Excellent observation from the peaks of several hills allowed the German defenders to detect Allied movement and direct highly accurate artillery fire, preventing any northward advance. Running across the Allied line was the fast flowing Rapido River, which rose in the central Apennine Mountains, flowed through Cassino (joining to the Gari River, which was erroneously identified as the Rapido) and across the entrance to the Liri valley. There the Liri river joined the Gari to form the Garigliano River, which continued on to the sea. With its heavily fortified mountain defences, difficult river crossings, and valley head flooded by the Germans, Cassino formed a linchpin of the Gustav Line, the most formidable line of the defensive positions making up the Winter Line. In spite of its potential