Vignola's knowledge of Michelangelo's intentions, little happened in this period. In 1585 the energetic Pope Sixtus V appointed Giacomo della Porta who was to be assisted by Domenico Fontana. The five-year reign of Sixtus was to see the building advance at a great rate. Michelangelo left a few drawings, including an early drawing of the dome, and some details. There were also detailed engravings published in 1569 by Stefan du Pérac who claimed that they were the master's final solution. Michelangelo, like Sangallo before him, also left a large wooden model. Giacomo della Porta subsequently altered this model in several ways. The major change restored an earlier design, in which the outer dome appears to rise above, rather than rest directly on the base. Most of the other changes were of a cosmetic nature, such as the adding of lion's masks over the swags on the drum in honour of Pope Sixtus and adding a circlet of finials around the spire at the top of the lantern, as proposed by Sangallo. A drawing by Michelangelo indicates that his early intentions were towards an ovoid dome, rather than a hemispherical one. In an engraving in Galasso Alghisi' treatise (1563), the dome may be represented as ovoid, but the perspective is ambiguous. Stefan du Pérac's engraving (1569) shows a hemispherical dome, but this was perhaps an inaccuracy of the engraver. The profile of the wooden model is more ovoid than that of the engravings, but less so than the finished product. It has been suggested that Michelangelo on his death bed reverted to the more pointed shape. However, Lees-Milne cites Giacomo della Porta as taking full responsibility for the change and as indicating to Pope Sixtus that Michelangelo was lacking in the scientific understanding of which he himself was capable. Helen Gardner suggests that Michelangelo made the change to the hemispherical dome of lower profile in order to establish a balance between the dynamic vertical elements of the encircling giant order of pilasters and a more static and reposeful dome. Gardner also comments, "The sculpturing of architecture [by Michelangelo] ... here extends itself up from the ground through the attic stories and moves on into the drum and dome, the whole building being pulled together into a unity from base to summit." It is this sense of the building being sculptured, unified and "pulled together" by the encircling band of the deep