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.
Pope Julius II
Pope Julius II commissioned the rebuilding of St. Peter's Basilica, Michelangelo's decoration and full-scale painting of the ceiling of the Sistine Chapel, and his discerning eye in hiring the artist Raphael as a young man brought numerous improvements to the Vatican.