By the early 1500s, the 4th-century Old St. Peter’s Basilica was considered structurally worn and no longer matched the papacy’s ambitions for Rome. Pope Julius II decided to replace it with a new, monumental church, setting up one of the largest building campaigns of the Renaissance.
A ceremonial beginning for the new building took place when the foundation stone was laid, marking the formal start of construction. Donato Bramante’s early concept emphasized a centralized plan (a “Greek cross,” with arms of equal length) intended to create a unified space under a great dome.
Bramante died before his plan could be fully carried out, leaving only early structural work and key layout decisions completed. His death triggered a long period of redesigns under successive architects, as each tried to solve the same basic challenge: how to build an enormous domed church safely and coherently.
Raphael was confirmed as architect of the new basilica, and his proposals shifted the design toward a longer church (adding more “nave,” the main aisle). This change reflected a growing desire to combine a grand central dome with a more traditional, processional layout for large ceremonies.
Imperial troops sacked Rome, causing widespread destruction, economic collapse, and a shock to papal authority. The event slowed major projects and helped end the optimistic “High Renaissance” atmosphere that had encouraged ambitious building and artistic commissions.
Antonio da Sangallo the Younger became the key architect for St. Peter’s and developed an elaborate solution, including extensive structural and exterior elements. A large wooden model was built to present and test his approach, showing how Renaissance builders used models to communicate designs at full scale.
After Sangallo’s death, Pope Paul III appointed Michelangelo to take charge of the project. Michelangelo pushed back against overly complicated additions and worked to restore a clearer, more unified plan centered on the crossing and dome-supporting piers.
Michelangelo advanced the structural and visual concept of the central dome and the massive supports beneath it. Although he did not live to see the dome finished, his model and design decisions became the main reference point for later architects and builders.
Pope Sixtus V pushed the project forward by appointing Giacomo della Porta and Domenico Fontana to build the dome based on Michelangelo’s model. They began the difficult masonry work in 1588, adjusting details to improve stability while keeping the overall concept recognizable.
By 1590, the dome’s main shell had been completed up to the base of the lantern (the small structure that crowns a dome). Finishing the dome was a major turning point: it made St. Peter’s skyline-defining form visible and allowed planning to shift toward completing the long interior spaces.
With the central area increasingly usable, Pope Clement VIII consecrated the main altar in 1594. This step shows that parts of the new basilica were becoming liturgically functional even while large-scale construction continued elsewhere.
Under Pope Paul V, Carlo Maderno redirected the project toward a longer, more ceremonial plan by extending the nave, turning the building into a “Latin cross” (a longer main axis). Maderno also began the façade, which would become the public face of the basilica and a clear signal that completion was in sight.
The façade campaign formally advanced when the first stone was laid in early 1608. Building the façade required integrating new construction with the enormous existing structure behind it, while also creating a monumental frontage suited to papal ceremonies and large crowds.
By 1612, most façade work was completed, and the inscription explicitly credited Pope Paul V. The project then continued with finishing details, including ornament and statues, reflecting the typical pattern of Renaissance construction: major masonry first, followed by decorative completion.
After 120 years of planning, redesign, and building, Pope Urban VIII consecrated the new St. Peter’s Basilica, marking it as officially complete for worship. While decoration and later additions continued in subsequent decades, the consecration set a clear endpoint for the main 1506–1626 construction story.
Construction History of St. Peter's Basilica, Rome (1506–1626)