The Last Supper (Leonardo)

True fresco, the standard mural technique of Leonardo's era, requires an artist to paint quickly onto wet plaster, which absorbs the pigment as it dries and binds it permanently into the wall. That speed did not suit Leonardo's working method, which favored slow reworking, layering and correction over rapid, irreversible strokes. So for The Last Supper he abandoned fresco entirely and painted in tempera and oil directly onto dry plaster instead, a technique that let him work at his own pace but that never chemically bonded the paint to the wall the way true fresco does.

The consequences arrived almost immediately. Within about twenty years of its completion around 1498, visitors were already recording that the paint was flaking and discoloring, and by the mid-sixteenth century, roughly fifty years after Leonardo finished it, one observer described the work as already so ruined that the figures could barely be made out. The refectory's location in a low, damp part of Milan, prone to flooding, made the underlying wall itself an unstable surface for anything painted on it, compounding the technique's own weaknesses.

The mural has been restored repeatedly since, most extensively in a twenty-two-year conservation project completed in 1999, which removed centuries of earlier repainting and grime to reveal what could still be recovered of Leonardo's original surface underneath. What museum visitors see today is consequently not simply a five-hundred-year-old painting but the end result of an unusually long and difficult conservation history, layered on top of a technique that began working against itself almost from the moment it was finished.

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.