Many of Bramante’s drawings can be found in the Uffizi Gallery in Florence. All of them have one feature in common: a square design with a Greek cross and four prominent apses. The square forms a cubical space and is covered in the centre by a hemispheric dome. According to Arnaldo Bruschi (1984), the structure has a precise symbolism, which can be “schematised – in accord with an ancient, mostly Byzantine tradition – as a cube (the world) with four extending arms (the four parts of the world), and a dome above it (heaven).”
Work on the first pylon began with great ceremony on 18th April 1506, and foundations for the other three pylons were laid the following year. Construction halted, however, when Julius II (1513) and Bramante (1514) died; by then the basilica had reached the top of the four pylons. Several other proposals for St Peter’s were drawn up over the next 40 years, in the midst of heated debate over whether the new St Peter’s should have a central or longitudinal plan. Bramante and other Renaissance architects preferred the central plan, but the longitudinal plan or Latin cross conformed more to ecclesiastic tradition and would also cover the entire area of the ancient Constantinian basilica. As the four central pylons had already been built, Raphael (1514) and Antonio da Sangallo the Younger (1538) proposed a longitudinal plan, while Baldassarre Peruzzi (1520) favored a central plan. Finally in 1547, Pope Paul III commissioned Michaelangelo to propose a new design. His solution was to keep Bramante’s original plan, thickening the pilasters and the external walls and creating niches and ledges by chiselling out the walls.
A vast dome was to cover the central area, where the papal altar was to be placed. The building was finished, although the dome was not completed at Michelangelo’s death in 1564. His pupil, Giacomo della Porta, finished building it with a few changes, such as raising the curve of the calotte. The dilemma over choosing between a central or a longitudinal plan was not yet definitely resolved, however. The Council of Trent, which ended in 1563, expressed a preference for longitudinal churches. Carlo Maderno was therefore asked to extend Michelangelo’s original plan.
He achieved this by adding two bays, turning St Peter’s floor plan into a Latin cross. Maderno also designed St Peter’s “classical” façade, built between 1607 and 1612. Unfortunately it tended to hide Michelangelo’s dome and reduce its visual impact. Bernini’s square sought to resolve the problem with an optical effect that draws the dome forward.