Montecassino is a rocky hill about 130 kilometres (81 mi) southeast of Rome, Italy, c. 2 kilometres (1.2 mi) to the west of the town of Cassino (the Roman Casinum having been on the hill) and 520 m (1,706.04 ft) altitude. St. Benedict of Nursia established his first monastery, the source of the Benedictine Order, here around 529.
According to Gregory the Great's biography of Benedict, Life of Saint Benedict of Nursia, the monastery was constructed on an older pagan site, a temple of Apollo that crowned the hill. The biography records that the area was still largely pagan at the time and Benedict's first act was to smash the sculpture of Apollo and destroy the altar. He then reused the temple, dedicating it to Saint Martin, and built another chapel on the site of the altar dedicated to Saint John the Baptist. Archaeologist Neil Christie notes that it was common in such hagiographies for the protagonist to encounter areas of strong paganism. Once established at Monte Cassino, Benedict never left. There he wrote the Benedictine Rule that became the founding principle for western monasticism. There at Monte Cassino he received a visit from Totila, king of the Ostrogoths, perhaps in 543 (the only remotely secure historical date for Benedict), and there he died.
Monte Cassino became a model for future developments. Unfortunately its prominent site has always made it an object of strategic importance. It was sacked or destroyed a number of times. In 581, during the abbacy of Bonitus, the Lombards sacked the abbey, and the surviving monks fled to Rome, where they remained for more than a century. During this time the body of St Benedict was transferred to Fleury, the modern Saint-Benoit-sur-Loire near Orleans, France.
In December 1942, some 1,400 irreplaceable manuscript codices, chiefly patristic and historical, in addition to a vast number of documents relating to the history of the abbey and the collections of the Keats-Shelley Memorial House in Rome, had been sent to the abbey archives for safekeeping. Fortunately, German officers Lt. Col. Julius Schlegel (a Roman Catholic) and Capt. Maximilian Becker (a Protestant), both from the Panzer-Division Hermann Göring, had them transferred to the Vatican at the beginning of the battle.
During the Battle of Monte Cassino (January - May 1944) the Abbey made up one section of the 161 kilometre (100 miles) Gustav line, which was a defensive German line designed to hold the Allied attackers from advancing any further into Italy during World War Two. It stretched from coast to coast and the monastery was one of the key strongholds overlooking highway 6 and blocking the path to Rome. On 15 February 1944 the abbey was almost completely destroyed in a series of heavy American led air-raids. The bombing was conducted because many reports from troops on the ground suggested that Germans were occupying the monastery, and it was considered a key observational post by all those who were fighting in the field. However, actually during the bombing no Germans were present. It is certain from every investigation that followed since the event that the only people killed in the monastery by the bombing were 230 Italian civilians seeking refuge in the abbey. After the bombing the ruins of the monastery were occupied by German Fallschirmjäger, aiding them in their defense, because the ruins provided excellent defensive cover. The heavily outnumbered Germans held the position until withdrawing on 17 May 1944, having repulsed four main offensives by the New Zealanders, British Indian division and Polish corps. Allied forces broke the line between 11 and 17 May. The Polish 12th Podolian Uhlans Regiment of the Polish II Corps, commanded by Lt. Gen. Władysław Anders, raised the Polish flag over the ruins 18 May 1944. The road to Rome was then open.
The Abbey was rebuilt after the war; Pope Paul VI reconsecrated it in 1964. During reconstruction, its library was housed at the Pontifical Abbey of St Jerome-in-the-City.