How did Michelangelo contribute to the design of St. Peter’s Basilica in Rome?

Michelangelo made significant contributions to the design of St. Peter’s Basilica after becoming the project's architect in 1547. His work focused on both the structural and aesthetic unification of the building:12

• Restoring the Central Plan: Michelangelo rejected the modifications made by his predecessors and reverted to the original Greek cross plan envisioned by Donato Bramante, which featured four equal arms around a central dome.34
• The Dome: He designed the massive 390-foot-high dome intended to sit directly above the tomb of St. Peter. While the dome was constructed after his death by Giacomo della Porta and Domenico Fontana—who made it taller and steeper than his original design—it remains a defining visual element of his architectural legacy.1234
• Exterior and Interior Design: Michelangelo unified the interior space and designed the exterior walls with colossal pilasters that created a sense of "pulsing dynamism". He also incorporated a columned walkway around the base of the dome, which functioned structurally like Gothic flying buttresses to support the dome's weight while maintaining a classical aesthetic.4