Of the present scheme of frescos, the earliest part is that of the side walls. They are divided into three main tiers. The central tier of the walls has two cycles of paintings, which complement each other, "The Life of Moses" and "The Life of Christ". They were commissioned in 1480 by Pope Sixtus IV and executed by Domenico Ghirlandaio, Sandro Botticelli, Pietro Perugino, Cosimo Rosselli and their workshops. They originally ran all round the walls, but have since been replaced on both end walls.