by mutability and corruptibility in contrast with the perfect and eternal world of heaven represented by the mosaics of the dome above. Sebastiano del Piombo: Birth of the Virgin John Shearman proposed that the main altar-piece was intended to be an Assumption of the Virgin but the theory remains heavily disputed. Soon after Raphael died, Sebastiano del Piombo was chosen to carry on the work on the altar-piece but he achieved less than expected. Vasari gives a scathing account in his Lives: "He did little work there, although we find that he obtained from the liberality of Agostino and his heirs much more than would have been due to him even if he had finished it completely, which he did not do, either because he was weary of the labors of art, or because he was too much wrapped up in comforts and pleasures." During this decade Sebastiano may have produced several drafts to the patrons. Two of them survived: an earlier preparatory study in the Kupferstichkabinett Berlin and a finely executed, definitive modello drawing in the Louvre. The main difference is that the group in the upper part of the painting (God and angels) is missing on the earlier Berlin drawing. The composition of the modello, which is identical to the executed mural, became more mature and harmonious. (Another study, a small drawing of a female head, was acquired by the Louvre in 2004.) On 1 August 1530 Filippo Sergardi, who was guardian to the heirs of Agostino Chigi, signed a new contract with Sebastiano accepting the final version. In this document the artist was entrusted to paint the altar-piece and the other murals in the next three years for a compensation of 1500 plus 1300 gold ducats. The Birth of the Virgin was eventually begun by Sebastiano del Piombo using an unusual technique, oil on peperino stone blocks. This was invented by him and greatly admired by his contemporaries. The mural was left unfinished by Sebastiano in 1534 and it was completed by Francesco Salviati by 1554. The upper part with the figure of the Holy Father and the angels is mainly Salviati's work. The iconography of the painting is rather unusual. According to Costanza Barbieri the presence of God in the upper part combines the traditional subject of the nativity with the doctrine of the Immaculate Conception which was still not generally accepted but it was heavily