In the winter of 1943 General Albert Kesselring withdrew his forces to what became known as the Gustav Line on the Italian peninsula south of Rome. Organized along the Garigliano and Rapido rivers it included Monte Cassino, a hilltop site of a sixth-century Benedictine monastery. Defended by 15 German divisions the line was fortified with gun pits, concrete bunkers, turreted machine-gun emplacements, barbed-wire and minefields. In December 1943, the Allied suffered heavy loses while trying to capture Monte Cassino.
General Harold Alexander, Supreme Allied Commander in Italy, ordered a new Cassino offensive combined with an amphibious operation at Anzio, a small port on the west coast of Italy. The main objective of the operation was to cut the communication lines of the German 10th Army and force withdrawal from the Gustav Line.
On 12th February the exhausted US Army at Cassino were replaced by the New Zealand Corps. Alexander now decided to use these fresh troops in another attempt to capture Cassino. General Bernard Freyberg, who was in charge of the infantry attack, asked for the monastery be bombed. Despite claims by troops on the front-line that no fire had come from the monastery, General Harold Alexander agreed and it was destroyed by the United States Air Force on 15th February, 1944.
Once the monastery had been bombed, the German Army moved into the ruins. As Basil Liddell Hart pointed out later in his book The Other Side of the Hill the bombing "turned out entirely to the tactical benefit of the Germans. For after that they felt free to occupy the ruins, and the rubble provided mud better defensive cover than the Monastery would have been before its destruction. As anyone with experience of street-fighting knows, it is only when buildings are demolished that they are converted from mousetraps into bastions of defence."
After the bombing the Germans were able to halt several attempts to capture Monte Cassino. It was not until troops led by General Wladyslaw Anders (Polish Corps) and General Alphonse Juin (French Corps) that the monastery was taken on 18th May, 1944.