is entirely Gothic, its engineering was highly innovative, and the product of a mind that had studied the huge vaults and remaining dome of Ancient Rome. Sangallo's plan (1513), of which a large wooden model still exists, looks to both these predecessors. He realized the value of both the coffering at the Pantheon and the outer stone ribs at Florence Cathedral. He strengthened and extended the peristyle of Bramante into a series of arched and ordered openings around the base, with a second such arcade set back in a tier above the first. In his hands, the rather delicate form of the lantern, based closely on that in Florence, became a massive structure, surrounded by a projecting base, a peristyle and surmounted by a spire of conic form. According to James Lees-Milne the design was "too eclectic, too pernickety and too tasteless to have been a success". Michelangelo and Giacomo della Porta, 1547 and 1585 Michelangelo redesigned the dome in 1547, taking into account all that had gone before. His dome, like that of Florence, is constructed of two shells of brick, the outer one having 16 stone ribs, twice the number at Florence but far fewer than in Sangallo's design. As with the designs of Bramante and Sangallo, the dome is raised from the piers on a drum. The encircling peristyle of Bramante and the arcade of Sangallo are reduced to 16 pairs of Corinthian columns, each of high which stand proud of the building, connected by an arch. Visually they appear to buttress each of the ribs, but structurally they are probably quite redundant. The reason for this is that the dome is ovoid in shape, rising steeply as does the dome of Florence Cathedral, and therefore exerting less outward thrust than does a hemispherical dome, such as that of the Pantheon, which, although it is not buttressed, is countered by the downward thrust of heavy masonry which extends above the circling wall. The ovoid profile of the dome has been the subject of much speculation and scholarship over the past century. Michelangelo died in 1564, leaving the drum of the dome complete, and Bramante's piers much bulkier than originally designed, each across. Following his death, the work continued under his assistant Jacopo Barozzi da Vignola with Giorgio Vasari appointed by Pope Pius V as a watchdog to make sure that Michelangelo's plans were carried out exactly. Despite