A protective sandbag wall was built around The Last Supper in 1940 during World War II.
Italian art officials anticipated that Allied bombing could destroy Santa Maria delle Grazie and placed sandbags, wooden or pine scaffolding, and metal bracing around the wall carrying Leonardo’s mural. The defenses were intended to absorb blast effects and keep falling masonry from crushing the painting.
The precaution proved crucial on 15 August 1943, when Allied bombs struck the complex. The refectory’s roof and other walls collapsed, but the reinforced wall containing The Last Supper remained standing. The mural was still exposed to weather afterward, however, and the vibration and humidity caused additional conservation problems.
The sandbags did not restore the painting or make it undamaged. They simply helped it survive a direct wartime catastrophe. Postwar treatments, including Mauro Pellicioli’s work from 1946 to 1954, stabilized the surface before the much more extensive 1978–1999 restoration.