The New St. Peter’s Basilica

The New St. Peter’s Basilica

The New St. Peter’s Basilica in Vatican City was designed as a three aisles Latin cross containing a dome at the intersection which is located over the high alter that shelters the shrine to St.Peter the apostle. The original idea of the church came from Pope Nicholas V when the walls of the old St. Peter's basilica were found covered in dust. Upon the discovery in 1492, the Pope ordered Bernardo Rossellino to construct a new apse. The construction came to a halt when the Pope died. The responsibility later fell to Paul II. Paul II entrusted the project to Giuliano da Sangallo in 1470. It wasn't until 1506 that the first stone of the new basilica was laid. The new basilica was designed to form a Greek Cross, but under the switches in control, the Greek cross evolved into a Latin cross with three aisles separated by pillars. "After the sack of Rome in 1527, Paul III (1534–49) entrusted the undertaking to Antonio da Sangallo the Younger, who returned to Bramante’s plan (Greek Cross) and erected a dividing wall between the area for the new basilica and the eastern part of the old one, which was still in use." When Sangallo died in 1546, Michelangelo became chief architect and followed through until his death and by that time the drum of the dome was almost complete. "Paul V (1605–21) adopted Carlo  Maderno’s plan, giving the basilica the form of a Latin cross by extending the nave to the east, thus completing the 615-foot- long mainstructure. Maderno also completed the facade of St. Peter’s and added an extra bay on each end to support campaniles. Although Maderno left designs for these campaniles, only one was built, and that was of a different design executed by Gian Lorenzo Bernini in 1637". Finally, in 1655-1657, Bernini designed the elliptical piazza, outlined by colonnades, that serves as the approach to the basilica.

https://www.britannica.com/topic/Saint-Peters-Basilica
A History Of Architecture On The Comparative Method, Fletcher, Banister