Final answer:
Pope Julius II commissioned Donato Bramante to design the new St. Peter's Basilica, which was later altered by architects such as Raphael and Michelangelo, with Michelangelo credited for the final design of the Basilica.
Step-by-step explanation:
Pope Julius II decided to replace the ancient St. Peter's Basilica with a monumental structure to house his enormous tomb and to reflect the greatness of his tenure. He commissioned Donato Bramante to design the new basilica in 1505, opting to demolish the old basilica that stood since the fourth century. Bramante proposed a building with a Greek Cross plan, but after his death, the project saw a number of different architects including Raphael and Michelangelo, who both made significant changes to Bramante's original plan. However, Michelangelo is credited with the final design of the Basilica, particularly the symmetrical Greek Cross form.