Battle of Monte Cassino
Following initial British and Canadian beachheads in Calabria and the American invasion of the Salerno/Naples area, the Allied drive north toward Rome proved hard to do. Both the west coast route and the Route 6 central mountain route were blocked by the Germans. In late 1943, after a fierce battle at San Pietro, a stalemate developed south of the German Winter Line, a set of three defensive perimeters of interlocking bunkers and fortifications that sealed off southern Italy. In addition to German defenses, severe weather during December 1943 – January 1944 created tens of thousands of casualties in the harsh Italian mountain terrain.
The Gustav Line, the northernmost and most formidable of three German Winter Line defensive belts, was anchored by Monte Cassino and the Garigliano and Rapido Rivers. The town of Cassino, about 85 miles southeast of Rome, was a mile east of Monte Cassino.
The Germans built heavily fortified emplacements and observation posts next to the St. Benedict Monastery walls on Monte Cassino, taking full advantage of the terrain and Allied reluctance to attack the Abbey. Allied planners had to treat the entire hilltop as a key military target, dominating the Cassino valley, and the obstacle to their objective of cracking the Gustav Line.
First Battle of Cassino
The Allies launched their offensive on the Gustav Line on 12 January 1944, with the French Expeditionary Corps assaulting Cassino and the British 10 Corps attempting to exploit previous gains on the Garigliano River. Neither attack succeeded in breaking through, although limited progress was made. One week later, on 20 January, the U.S. II Corps attacked in the center of the Fifth Army front, attempting to cross the Rapido River. After two days of bitter fighting and heavy losses, the II Corps’ 36th Infantry Division was forced to break off its attack. The expected rapid breakthrough became a bloody war of attrition. The U.S. 34th Division lost 2,200 men attempting to penetrate German prepared defenses on the Rapido River, failing in attempts to cross the river valley under German fire directed from Monte Cassino. The other Allied forces did a little better, crossing to the north of the Rapido, but were ultimately forced to withdraw.
Second Battle of Cassino
After considerable debate and delay due to fear of offending Christians worldwide, the Allies decided the monastery had to be bombed to dislodge the Germans. After trying leaflets urging the Germans to abandon the site, on 15 February 1944 American bombers dropped 1,150 tons of high explosives and incendiary bombs on the Abbey, reducing the entire top of Monte Cassino to smoking rubble. A simultaneous ground assault went on for three days, attempting to reach the high ground of the monastery. The Germans held on to the mountain top, although the Commonwealth troops from New Zealand and India were successful in capturing some ground in and around Cassino. However, with the Germans continuing to hold the high ground of Monte Cassino, there was little chance of expanding the gains. The Germans actually had suffered very heavy casualties, but this was unknown to the Allies at the time.
Third Battle of Cassino
For another month, inconclusive ground fighting in wet weather continued around Hill 516, leading to another bomb run, this time with 500 planes dropping 1,400 tons of bombs on Cassino and the mountain on 15 March 1944. The town of Cassino was flattened by the bombing and artillery bombardment. Despite the heavy damage, again the German defenders clung to the ruins, actually improving their defenses in the rubble left by the bombings. About 75% of the town was in Allied hands by this time, but Allied troops could not fully overcome the stubborn resistance that went on building by building in town and yard by yard in the surrounding rugged terrain. German positions remained intact and were vigorously defended. Mechanized war with tanks was impossible in the rugged terrain and amid the bombing debris, forcing hand to hand combat by soldiers supplied by mules.
Fourth Battle of Cassino
Cassino was finally taken in Operation DIADEM, the Allied spring 1944 offensive in Italy, beginning on 11 May under the overall command of General Sir Harold Alexander. Using a well coordinated combined force of infantry backed up by bombing and artillery, the Gustav Line was finally breached on 14 May. US Fifth Army to the south and west and the British Eighth Army in the center combined in a dual strike while VI US Corps at Anzio finally broke out along the coast and to the rear of the Gustav Line. Eighth Army succeeded in cutting Highway 6, the main road linking the south of Italy to Rome.
On Monte Cassino itself, two divisions of the II Polish Corps battled the German 1st Parachute Division for the mountain. After days of attacks and counterattacks in hand to hand fighting, on the night of 17 May the German garrison abandoned Monte Cassino as part of a general German retreat from the Gustav Line to new defensive lines to the north. At 10:30 in the morning, 18 May 1944, the Polish flag was raised over the Monte Cassino rubble, ending the battle.
Allied troops continued the drive north, capturing Rome on 4 June 1944.

It is estimated that there were 20,000 Allied casualties in the series of battles. The Monastery itself was reconstructed after World War II and was reconsecrated by Pope Paul VI in 1964.