Santa Maria del Popolo
The architect or architects of this innovative project remain unknown due to a lack of contemporary sources. Giorgio Vasari in his "Lives" attributed all the important papal projects in Rome during Sixtus IV to a Florentine, Baccio Pontelli including the basilica and monastery of Santa Maria del Popolo. Modern researchers deemed this claim highly dubious and proposed other names among them Andrea Bregno, a Lombard sculptor and architect whose workshop certainly received important commissions in the basilica. The fundamental differences between the façade and the interior suggest that maybe more than one architect was working on the building.
Giuliano da Sangallo
Giuliano's final work was to assist in the design and construction of the new St. Peter's Basilica. Sangallo was called upon to design the large dome atop the basilica. Pope Julius II, however, chose the design of Donato Bramante instead and construction began in 1506. The dome was influenced by the dome atop the Florence Cathedral which was designed by Bramante and Sangallo's role model, Filippo Brunelleschi. After Giuliano's distinguished career and close working relationship with Pope Julius II, Bramante's promotion left him devastated and he left Rome for Florence. After the death of Julius II and the subsequent election of Giovanni de' Medici to the papacy in 1513 as Pope Leo X, along with the death of Bramante in 1514, Giuliano was recalled to Rome from Florence to help rebuild the basilica. By this time however, Giuliano was over seventy years old and not well enough to travel back to Rome and oversee a project of such magnitude. Therefore, Pope Leo X selected another distinguished artist, Raphael, to assume control of the design of the new basilica.