In the same year (1506), Pope Julius conceived a program to paint the ceiling of the Sistine Chapel. The walls of the chapel had been decorated twenty years earlier. The lowest of three levels is painted to resemble draped hangings and was (and sometimes still is) hung on special occasions with a set of tapestries designed by Raphael. The middle level contains a complex scheme of frescoes illustrating the Life of Christ on the right side and the Life of Moses on the left side. It was carried out by some of the most renowned Renaissance painters: Botticelli, Ghirlandaio, Perugino, Pinturicchio, Signorelli and Cosimo Rosselli. The upper level of the walls contains the windows, between which are painted pairs of illusionistic niches with representations of the first 32 popes. A draft[clarification by Pier Matteo d'Amelia indicates that the ceiling was painted blue like that of the Arena Chapel and decorated with gold stars, possibly representing the zodiacal constellations. It is probable that, because the chapel was the site of regular meetings and Masses of an elite body of officials known as the Papal Chapel (who would observe the decorations and interpret their theological and temporal significance), it was Pope Julius' intention and expectation that the iconography of the ceiling was to be read with many layers of meaning.