The abbey was dissolved by the Italian government in 1866. The building became a national monument with the monks as custodians of its treasures. In 1944 during World War II, it was the site of the Battle of Monte Cassino and the building was destroyed by Allied bombing.

The monastery was rebuilt in the postwar years and completed by 1964. The town had been pulverised and the plain was a cratered wilderness. In fact, so great was the damage that a new town was created on freshly drained land while nature gradually reclaimed the ruins of the old.