The strategic position of Monte Cassino has made it the repeated scene of battles and sieges from antiquity.

In World War II, the Battle of Monte Cassino (also known as the Battle for Rome) was a costly series of battles fought by the Allies with the intention of breaking through the Gustav Line, seizing Rome and linking up with Allied forces contained within the Anzio pocket.

The first battle started on January 4, 1944 and the monastery atop the hill was destroyed by Allied bombing on February 15. Allied aircraft heavily bombed the ruins of the monastery and staged an assault on March 15.

During three failed attempts to take the heavily-guarded monastery of Monte Cassino (January 17–25, February 15–February 18, March 15–March 25), the forces of the USA, the UK, India, Canada, Australia, South Africa and New Zealand lost approximately 54,000 men yet did not manage to seize the city or the castle overlooking the Rapido River valley.

The so-called Fourth Battle of Monte Cassino was fought by the 2nd Polish Corps under General Władysław Anders (May 11–May 19). The first assault (May 11–May 12) brought heavy losses but also allowed the British 8th Army under General Sir Oliver Leese to break through German lines in the Liri river valley below the monastery.

The second assault (May 17–May 19), carried out at immense cost by the Polish troops with the aid of a force under French fatigues of Moroccan hill tribesmen used for mountain warfare, pushed the German 1st Parachute Division out of its positions on the hills surrounding the monastery and almost surrounded them. In the early morning of May 18 a reconnaissance group of Polish 12th Podolian Uhlans Regiment occupied the ruins of the monastery after it was evacuated by the Germans.

The capture of Monte Cassino allowed the British and American divisions to begin the advance on Rome, which fell on June 4 1944 just two days before the Normandy invasion.

In the course of the battles the historic monastery of Monte Cassino, where St. Benedict first established the rule that ordered monasticism in the west, was entirely pulverized. Fortunately its irreplaceable library had been removed for safekeeping to Rome at the start of the Battle by the Germans. The site has since been rebuilt, but the historic buildings are utterly gone.

In 1961–1963 Piotra Sych wrote a novel about the battle called Death and nightingales (in Belarusian).