During World War II, the Keats–Shelley House went "underground", especially after 1943, in order to preserve its invaluable contents from falling into the hands of, and most likely being deliberately destroyed by, Nazi Germany. External markings relating to the museum were removed from the building. Although the library's 10,000 volumes were not removed, two boxes of artifacts were sent to the Abbey of Monte Cassino in December 1942 for safekeeping. In October 1943, the abbey's archivist placed the two unlabelled boxes of Keats–Shelley memorabilia with his personal possessions so that they could be removed during the abbey's evacuation and not fall into the hands of the Germans. The items were reclaimed by the museum's curator and returned to the Keats–Shelley House, where the boxes were reopened in June 1944 upon the arrival of the Allied forces in Rome.