The fresco you are about to meet was painted in 1447 by Andrea del Castagno. The lower part of the wall is given over entirely to the Last Supper, which the Tuscan museums authority describes as taking place in a richly decorated setting where every architectural element is rendered with meticulous detail. That is the first thing worth noticing: this is not a shallow stage. Castagno builds a room inside the room, with mouldings, panelled surfaces, and receding lines that seem to answer the real architecture around you. The specialist description of his manner is worth holding as you look: a pictorial language of extraordinary formal firmness, a severe and monumental vision, held in a balance that never gives up its inner tension. That is interpretation, yes, but it is the interpretation of people who know the painting closely. The cenacolo also displays other works by Castagno painted around the middle of the fifteenth century, including a lunette fresco of Christ in the Pietà among the angels, a Crucifixion, and the sinopia, the preparatory underdrawing, for a Vision of Saint Jerome with saints at his side. A sinopia is a kind of ghost: the drawing a fresco is built upon, normally buried beneath the finished plaster. Seeing one is like reading a painter's first sentence.