The barrel-vaulted ceiling is entirely covered by the famous frescoes which Michelangelo painted between 1508 and 1512 for Julius II. The original design was only to have represented the Apostles, but was modified at the artist's insistence to encompass an enormously complex iconographic theme which may be synthesized as the representation of mankind waiting for the coming of the Messiah. More than twenty years later, Michelangelo was summoned back by Paul III (1534-49) to paint the Last Judgement on the wall behind the altar. He worked on it from 1536 to 1541.