involved. An altogether different set of challenges lay in constructing the basilica itself—and above all its 448-foot dome. Bramante irrevocably set the proportions of the basilica by means of the four immense pillars supporting the dome. But in some ways, this was the easy part, for the challenge lay in building a dome to fit these pillars, a task begun by Michelangelo and finished by Giacomo della Porta. Here, the trials were altogether more complex than with the obelisk, for the forces at play