The Battle of Monte Cassino began when Allied forces launched the first of four attacks against the Gustav Line in Italy.
The Gustav Line, which together with the Bernhardt and Hitler lines formed a series of defences known as the Winter Line, had been established by the Germans and Italians to defend Rome from a northern advance by the Allies. The Allied forces had secured a foothold in Italy in Operation Avalanche the previous September, having first captured Sicily.
By early January 1944 the Allies had advanced a long way north, but their progress had been stopped by poor weather that forced them to approach Rome along Highway 6 that ran from Naples through the Liri valley. The southern entrance to the valley was dominated by the town of Cassino and overlooked by the Benedictine abbey of Monte Cassino.
Although the German army did not position defensive units in the abbey itself, the natural topography gave them a notable advantage over the Allies. Combined with minefields that had been laid in advance, the strong German position withstood the first assault that lasted for two and a half weeks and involved troops under British, American and French command attacking the position from three sides.
German forces finally withdrew on 17 May, and the following morning soldiers from the Polish 12th Podolian Cavalry Regiment raised a Polish flag over the ruins. The four assaults that made up the Battle of Monte Cassino had led to 55,000 Allied casualities and destroyed the ancient abbey. The treasures it contained had been evacuated to Rome in November 1943.