the nave of five bays, with a row of complex apsidal chapels off the aisles on either side. Raphael's plan for the chancel and transepts made the squareness of the exterior walls more definite by reducing the size of the towers, and the semi-circular apses more clearly defined by encircling each with an ambulatory. In 1520 Raphael also died, aged 37, and his successor Baldassare Peruzzi maintained changes that Raphael had proposed to the internal arrangement of the three main apses, but otherwise reverted to the Greek Cross plan and other features of Bramante. This plan did not go ahead because of various difficulties of both Church and state. In 1527 Rome was sacked and plundered by Emperor Charles V. Peruzzi died in 1536 without his plan being realized. At this point Antonio da Sangallo the Younger submitted a plan which combines features of Peruzzi, Raphael and Bramante in its design and extends the building into a short nave with a wide façade and portico of dynamic projection. His proposal for the dome was much more elaborate of both structure and decoration than that of Bramante and included ribs on the exterior. Like Bramante, Sangallo proposed that the dome be surmounted by a lantern which he redesigned to a larger and much more elaborate form. Sangallo's main practical contribution was to strengthen Bramante's piers which had begun to crack. On 1 January 1547 in the reign of Pope Paul III, Michelangelo, then in his seventies, succeeded Sangallo the Younger as "Capomaestro", the superintendent of the building program at St Peter's. He is to be regarded as the principal designer of a large part of the building as it stands today, and as bringing the construction to a point where it could be carried through. He did not take on the job with pleasure; it was forced upon him by Pope Paul, frustrated at the death of his chosen candidate, Giulio Romano and the refusal of Jacopo Sansovino to leave Venice. Michelangelo wrote, "I undertake this only for the love of God and in honour of the Apostle." He insisted that he should be given a free hand to achieve the ultimate aim by whatever means he saw fit. Michelangelo's contribution Michelangelo took over a building site at which four piers, enormous beyond any constructed since ancient Roman times, were rising behind the remaining nave of the old basilica. He also