The Last Supper

Leonardo's refectory mural, painted in a technique that started deteriorating within twenty years

Leonardo painted it between 1495 and 1498 on a dry wall using an experimental oil and tempera technique rather than true fresco, which allowed him to work slowly and doomed the picture almost immediately. It has been restored at least seven times, survived a bomb in 1943 that destroyed the rest of the refectory roof, and now sits in a climate-controlled room entered through airlocks.

You get fifteen minutes with twenty-four other people. It is enough. The composition organises twelve reactions to one sentence and you understand what it is doing within the first two minutes.