In 1563 the struggle became a tragic one. The head of the work at St. Peter's, Cesare de Casteldurante, was stabbed, and Pier Luigi Gaeta, Michelangelo's friend and one of his best aids, was thrown into prison on a false accusation of theft. Michelangelo responded to this by appointing Gaeta in Cesare's place. The committee of administration dismissed Gaeta and put Nanni in his place, and Michelangelo, beside himself with rage, no longer went to St. Peter's. His enemies did not lose this chance to spread the report that he was no longer willing to take charge of the building, and Michelangelo denied this in vain. The committee nominated a successor, and this successor was of course Nanni. Nanni cut loose at once from his master and began to give orders, for he thought that the old man of eighty-eight, weary at last of the struggle, would be forced either to submit or to resign. He did not know his antagonist. Michelangelo went at once to the pope and told him that if justice was not done he would leave Rome and go to Florence. The pope called the committee together and the members accused Michelangelo of having committed errors which endangered the whole building. Michelangelo asked for an investigation and summoned Nanni to show the mistakes of which he accused him. Nanni could show nothing but his own bad faith, and was dismissed in disgrace.[93] This did not prevent Nanni from sending, five months later, just after the death of Michelangelo, a letter by the Florentine ambassador to Cosmo de' Medici, asking again to be appointed his successor. Until his last hour Michelangelo met with this fierce opposition over the work on St. Peter's, but his faith and his fighting spirit found in this only another reason for persevering. While Michelangelo had taken Bramante's design for the church and rested on his authority, he had in the course of construction introduced many important modifications into the plan, and stamped the whole monument with the imprint of his own grandiose and heavy genius. He kept the Greek cross with equal arms and four apses, at the same time hiding the apse of the façade in a rectangular mass against which he wished to put a portico with four gigantic columns. He suppressed the salient angles and the towers which should have risen at the extremities of the four arms of the cross. The beautiful clean-cut lines of the curved ends of these arms, which in Bramante's plan stretched out in the form of a semicircular tribune, were smothered in a massive, vigorous envelope which gave the construction the effect of a fortified bastion. The most beautiful part of the work was the famous dome, where the influence of Brunelleschi combined with the conception of Bramante. Michelangelo said once while he was working on S. Lorenzo in Florence that "it was possible to do differently from Brunelleschi, but not to do better."