St. Peter's Basilica is the largest of all Roman Catholic churches and by any standards a grandiose achievement, but it inevitably suffered from the competing visions of all the architects called in to collaborate Bramante, Giuliano da Sangallo, Raphael, Baldassare Peruzzi, Michelangelo, Giacomo Della Porta, Domenico Fontana, and Carlo Maderno each adding, subtracting, and modifying, often with a pope looking over his shoulder.
The largest Roman Catholic church is St. Peter's Basilica.