On August 15, 1943, an Allied bombing raid struck Milan and hit the convent complex of Santa Maria delle Grazie directly, a high-explosive bomb landing close enough to the refectory that the building's roof collapsed, its cloister was destroyed, and entire walls came down around the room. By any ordinary measure, a fragile, already-deteriorating fifteenth-century mural in that room should not have survived.
It did, and the reason was neither luck nor the mural's own physical durability. City officials and architects in Milan, anticipating exactly this kind of wartime damage after Italy entered the Second World War in 1940, had already reinforced the specific wall carrying The Last Supper with sandbags, scaffolding and mattresses as a dedicated protective measure, treating the mural as a piece of cultural property worth actively shielding rather than simply hoping it would survive. When the rest of the refectory came down around it, that one reinforced wall held.
Workers clearing the rubble in the months afterward found the mural essentially intact beneath its protective covering, a striking outcome given how much of the surrounding structure was gone. The episode has become one of the more frequently cited examples of deliberate wartime art protection succeeding exactly as intended, a case where a specific, planned intervention, rather than chance, is what let a fragile five-hundred-year-old painting survive a direct wartime hit on the building that housed it.