massiveness, ponderous and sensuously splendid: idealizations, but of sensuous existence". By about 1515, Sebastiano had befriended and allied himself with Michelangelo, who recruited him "as a kind of deputy for him in painting", he having returned to his backlog of promised projects in sculpture. Michelangelo's intention was for Sebastiano to "contest Raphael's first place" in painting in Rome, using at least in part ideas and designs supplied by Michelangelo, whose rivalry with Raphael had become intense. The intention may have been for a closer relationship than actually resulted, as in 1516 Michelangelo returned to Florence, only returning occasionally to Rome for several years after. The first result of this collaboration was one of Sebastiano's most important paintings, a Pietà in Viterbo. Here the composition is highly unusual for this common subject (which Michelangelo had famously sculpted in 1498–99), with Christ lying across the bottom of the picture space, at the feet of a Virgin looking up to Heaven, so that the two figures do not actually touch. Though no drawing survives, this was Michelangelo's conception, where "an idea of high tragic power is expressed with extreme simplicity in a structure of severe geometric rigour". The back of the panels have large sketches in charcoal that seem to be by both artists. In 1516 he painted a similar subject, the Lamentation of Jesus (now Hermitage Museum) using his own composition, and showing his awareness of Raphael's handling of groups of figures. These led a Florentine friend of Michelangelo, Pierfrancesco Borgherini, to commission Sebastiano to decorate a chapel in San Pietro in Montorio in Rome; he no doubt hoped to get significant input from Michelangelo. There is a Michelangelo drawing of 1516 for the Flagellation of Jesus in the British Museum, and other sketches; the final design survives only in a copy by Giulio Clovio after another Michelangelo drawing (Royal Collection). In the event there were a series of interruptions and Sebastiano did not complete the chapel until early 1524. The Flagellation is painted in oil on plaster. This was a method first practiced by Domenico Veneziano, and afterwards by other artists; but according to Vasari only Sebastiano succeeded in preventing the colours eventually blackening. The last major work of the period was the Raising of Lazarus, now in the National Gallery, London, which was commissioned in 1516 by Cardinal Giulio de Medici, archbishop of Narbonne in southern France, and the future