Michelangelo, the Architect: Rome’s St. Peter’s Basilica

On Bramante‘s death in 1514 Raphael was entrusted with the direction of the new St. Peter’s basilica believing that he would be the one who could most faithfully develop such a project. Like Bramante, Raphael also came from Urbino and his career in the Pontifical Court, according to Vasari, had begun under the protection of the great architect. Raphael’s design changed the Basilica’s floor plan and wanted to include a wide nave of five bays, with a row of complex apsidal chapels off the aisles on either side. But Raphael wasn’t the most suitable genius for such a gigantic construction, and although the great Florentine architect Antonio da Sangallo assisted him, the works on St. Peter’s didn’t progress much. Finally, after Raphael died in 1520, his successor in the works of the Basilica was Baldassare Peruzzi, who kept the changes that Raphael had proposed to the internal arrangement of the three main apses, but reverted to the Greek Cross plan and other features designed by Bramante. Peruzzi’s plan did not go ahead because of various difficulties. In 1527 Rome was sacked and plundered, and Peruzzi died in 1536 without his plans for the Basilica being realized.

Raphael’s assistant, Antonio da Sangallo the Younger, proposed a plan which combined features of Peruzzi, Raphael and Bramante’s design. Sangallo’s main practical contribution to the works was to strengthen Bramante’s piers which had begun to crack. However, Sangallo died in 1546 and no one seemed capable of bringing the construction to fruition but Michelangelo, then in his seventies, his reputation growing more and more every day. On 1 January 1547 under the reign of Pope Paul III, Michelangelo succeeded Sangallo the Younger as the Capomaestro, the superintendent of the building program at St Peter’s. “After Antonio da Sangallo died in 1546,” says Vasari, “and as there was no one who directed the factory of Saint Peter, there were different opinions, until His Holiness, inspired by God, decided to entrust it to Michelangelo, who refused saying, to excuse himself from that burden, that his art wasn’t that of architecture. Finally, not admitting his scruples, the Pope ordered him to accept it, and so much against his will, he had to be in charge of that endeavor…”

Left: Floor plan of St. Peter’s Basilica projected by Raphael. Raphael envisioned a wide space with a nave of five bays, including rows of complex apsidal chapels off the aisles on either side. He also planned to reduce the size of the towers and to encircle each semi-circular apse with an ambulatory. Right: Floor plan for the Basilica projected by Michelangelo. Michelangelo considered the expensive project proposed by Sangallo (see picture below) too artificial and more in accordance to German architecture (spiers, ridges, etc.). He rejected Sangallo’s and Raphael’s ideas and returned to the central plan of the original project proposed by Bramante with the intention to further emphasize the impact of the dome.
The project of Antonio da Sangallo The Young for the Basilica of St. Peter. Sangallo’s project was a synthesis between Bramante‘s central plan solution and Raphael’s Latin cross (see picture above). Sangallo also wanted to include two high bell towers flanking the central dome, which also departed from the classical ideal of Bramante’s project.

Michelangelo suppressed countless details of Sangallo’s last project, numerous towers, spires and colonnades from the outside, which took away St. Peter’s original classical simplicity, but which, being a reason for considerable expenses, seemed to please the administrators of the architectural works and aroused the animosity of those who saw benefits in delaying the Basilica’s construction that so far had been lasted nearly half a century. To dispel all suspicion of sordidness, Michelangelo demanded that in the motu proprio (an edict personally issued by the Pope) in which he was appointed director of the works with full authority to do and undo, add and remove, it should be noted that he served the Church without any reward (monetary) and just for the love of God. Pope Paul III, who saw in the glorious sculptor the genius appropriate to finish the work, always supported Michelangelo against the intrigues of his enemies. “Your task”- said the sculptor to the administrators in the year 1551 – “is to make sure that the alms arrive and to see that they are not taken away by thieves; the plan and drawings of the church, on the other hand, are my sole responsibility.”

Michelangelo’s intervention in Saint Peter’s project consisted mainly in simplifying the floor plan, that is, to return to Bramante’s general idea, removing accessory elements that weakened the construction, as well as porticoes and openings that reduced the walls’ resistance. Instead, Michelangelo raised the dome to a much higher height than intended. Bramante had wanted to rebuild the Roman dome of the Pantheon, grandiose on the inside, but without a particular visual appealing on the outside. Michelangelo replaced it with a dome like that of Santa Maria del Fiore in Florence, and thus what he took away from the Basilica in extension, he gave it in height. Undoubtedly, what characterizes the exterior of the church of St. Peter in Rome today is its dome with its colossal height of 131 meters dominating the entire building.

General view of the Basilica of St. Peter as seen from Castel Sant’Angelo with Michelangelo’s dome rising behind Carlo Maderno’s baroque façade (completed n 1612).

Michelangelo redesigned St. Peter’s dome in 1547. Similar to the dome of Florence’s cathedral, St. Peter’s dome is built of two shells of brick, the outer one having 16 stone ribs, twice the number at Florence. Michelangelo’s dome is raised from the Basilica’s huge Bramante’s piers on a drum and is in the exterior encircled by a peristyle of 16 pairs of Corinthian columns, each of 15 meters (49 ft) high and connected by an arch. Also, taking from the design of Santa Maria del Fiore, St. Peter’s dome is ovoid in shape, rising steeply and therefore exerting less outward thrust than a hemispherical dome does (like that of the Pantheon).

Model for the dome of the Basilica of St. Peter, lime wood, 1560, 500 x 400 x 200 cm (Musei Vaticani, Vatican City). These are two views of the original wood model for the dome of St Peter’s (right, exterior and left, interior). When he was about 85 years old, Michelangelo ordered a carpenter to prepare a large wooden model of the dome based on a clay model he himself had produced in order to test his architectural project. Upon observation of this model, it’s apparent that Michelangelo’s successors in the construction kept more or less closely to the original design. Some deviations are confined mainly to three particular features: 1) instead of keeping the proposed self-contained triangular window cornices on the drum, they alternate them with segment cornices (see picture below); 2) between the ribs of the vaulting now run three concentric and ascending groins to each section, breaking and enlivening the bare, vaulted surfaces (in the design they were missing, the surfaces were smooth); 3) the consoles of the attic above the drum have been omitted. Michelangelo’s cupola is the apotheosis of the Romanesque and the Gothic arch, with a lantern that in spite of its classical columns and candelabra reminds us of a belfry of a bell tower.
View of the dome of St Peter’s Basilica in Vatican City, completed in 1590. Michelangelo projected this dome in a slightly pointed form. As with Brunelleschi’s dome in Florence, the pointed shape exerts less thrust than an hemispherical dome. Though designed by Michelangelo, the dome was built between 1585 and 1590 by Giacomo della Porta with the assistance of Domenico Fontana, who was probably the best engineer of the day, both closely following Michelangelo’s designs. Michelangelo was able to supervise, and follow, the dome’s construction from 1554-1557 up to the raising of the drum.

Michelangelo died in 1564, when only the base of the cupola had been built, but he left a detailed wooden model still preserved. The work on the dome continued under Michelangelo’s assistant Jacopo Barozzi da Vignola with Giorgio Vasari appointed by Pope Pius V as a supervisor to make sure that Michelangelo’s plans were carried out exactly. Despite all, the construction advanced little during this period. In 1585 the energetic Pope Sixtus V appointed Giacomo della Porta (assisted by Domenico Fontana), as Michelangelo’s successor in the direction of the works. Giacomo, in fact, was Michelangelo’s favorite disciple. Most of the changes della Porta considered on Michelangelo’s design for the dome were of a cosmetic nature, such as the addition of lion’s masks over the swags on the drum in honor of Pope Sixtus and adding a circlet of finials around the spire at the top of the lantern, as previously proposed by Sangallo. He also gracefully altered the design of the upper lantern, making it richer and more complicated, almost baroque in appearance. This slightly more modern detail placed on top of the curved gray surface of the dome covered with sheets of lead, completed the beauty of this magnificent work.

The lantern crowning the dome of St. Peter’s Basilica was completed by the architect Domenico Fontana. The cross raising on top contains two lead caskets housing relics: a fragment of the True Cross, a relic of St. Andrew and medallions of the Holy Lamb.

Giacomo della Porta and Domenico Fontana finally completed the dome in 1590, the last year of the pontificate of Sixtus V. His successor, Gregory XIV, oversaw Fontana complete the lantern and had an inscription to the honor of Sixtus V placed around the dome’s inner opening. The next pope, Clement VIII, had the cross placed on top of the lantern, an event that was accompanied by the ringing of the bells of all the city’s churches. In the arms of the cross are set two lead caskets for relics, one containing a fragment of the True Cross and a relic of St. Andrew and the other containing medallions of the Holy Lamb. Around the dome, in the inside, is written in letters 1.4 meters (4.6 ft) high: TV ES PETRVS ET SVPER HANC PETRAM AEDIFICABO ECCLESIAM MEAM. TIBI DABO CLAVES REGNI CAELORVM (“… you are Peter, and upon this rock I will build my church. I will give you the keys of the kingdom of heaven” following Matthew 16:18–19). Also, Beneath the lantern is the inscription: S. PETRI GLORIAE SIXTVS PP. V. A. M. D. XC. PONTIF. V. (To the glory of St Peter; Sixtus V, pope, in the year 1590, the fifth of his pontificate).

View under St. Peter’s dome with the crossing. The dome was completed by the architects Giacomo della Porta and Domenico Fontana. The internal decoration features mosaic technique, like most of the basilica, and was started in 1593, three years after the completion of the dome. They were executed by Cavalier d’Arpino and Giovanni De Vecchi under the orders of Pope Clement VIII, their cartoons with the designs were simultaneously transposed into mosaic by the best mosaicists of the period. These mosaics include scenes with Christ, the apostles and busts of popes and saints. The mosaic program is divided into six zones starting at the base of the cupola (above the 16 windows of the drum), and they depict: 1) 16 pope-saints buried in the basilica; 2) figures of Christ, Virgin Mary, St. Paul, St. John the Baptist and the 12 Apostles; 3) angels bearing the instruments of Christ’s Passion; 4) heads of cherubim and seraphim in circular medallions; 5) angels, the custodians of St. Peter’s tomb; 6) heads of angels. Above it all there’s a ring in blue figuring a sky spangled with stars, and above it the lantern with a representation of God the Father in Glory.

Seen from afar, the dome of St. Peter’s Basilica stands out from the slightly uneven plain of Lazio, and it is what characterizes Rome’s landscape the most. As Rome is located to one side of the Vatican, the sun always sets behind the dome cutting out its silhouette against the dusk. For centuries, hundreds of Romans gather every evening on the terraces of the Pincian gardens, on the other side of the Tiber in front of the Vatican, to witness this superb spectacle offered by the conjunction of nature and human ingenious.

Back view of student priests lined up by a wall overlooking the city of Rome with a view of St. Peter, 1950’s photograph.
The dome of St. Peter’s Basilica draw against the Roman sky in dusk.

St. Peter’s dome is, truly, a moral entity endowed with its own spirit, so similar and yet so different from Florence’s dome and from all those other domes that were built later in its imitation.

Such was the influence that St. Peter’s dome had on artists that, from the middle of the 16th century onwards, there is no church, no matter how large or small, that doesn’t want to have its own dome as a testimony of admiration for that of Saint Peter in Rome. Not only in Italy, but in all the other countries where the Renaissance arrived, both in rural brick churches covered with stucco or in great monuments such as the Basilica of San Lorenzo de El Escorial in Spain and later in that of the Invalides in Paris, the same motif is always repeated: a church with a cross plan crowned with a dome on a cylindrical drum above the transept. Though Michelangelo’s dome drew heavily from the Gothic profile of the dome of Florence’s Cathedral almost ignoring the Classicism of the Renaissance, it prefigured the architecture of the Baroque perhaps more than any other building of the 16th century.

In addition to the dome it can be said that, with the exception of the façade, the entire exterior of St. Peter’s Basilica was Michelangelo’s work; the church projected by Bramante would have been completely different, with its multiple porticoes and open galleries. It is in the apse of St. Peter’s that Michelangelo’s own style as an architect is understood. The very high curved walls of the apses end in a very simple horizontal attic that runs around the entire temple, apparently supported by colossal Corinthian pilasters. In the smooth spaces, balconies and windows open up showing off their civil and secular designs, but so grandiose that give back the building its religious character that would have been lost if we just consider those openings almost domestic in appearance. Michelangelo’s work in St. Peter’s is generally obscured behind the baroque impression given by the square and the façade, both built much later; but when going around the Basilica, when seeing the huge church with its severe architecture of its walls, and when looking up to the very high cornice seeing those stone canvases unique in the world for its size and nobility, the viewer once again feels the same effect of religious emotion produced by the cathedrals of the Middle Ages. Once again Michelangelo managed, with his elevated artistic and personal spirit, to give a new mystical meaning to the lavish work originally intended to carry out by the mundane ambitions of the Rome of the Renaissance.

Basilica of St. Peter: side/back view, by Michelangelo, 1546-1564 (Vatican City). Michelangelo wrote a devastating letter criticizing the design of Antonio da Sangallo the Younger, then accepted the commission to complete St. Peter’s without pay, and developed a new, unified plan. He eliminated the ambulatories and the façade with towers (see picture above). The Greek-cross plan of Bramante was reinstated, along with the unifying colossal order on the exterior. In order to unify the exterior, Michelangelo used the Corinthian order as an embracing theme by pairing Corinthian pilasters in the lower mass of the church and pairing Corinthian columns in the peristyle and lantern of the dome (see pictures above). He designed a Florentine ribbed dome instead of Bramante’s hemisphere, dividing it by 16 ribs rather than the eight of the dome by Brunelleschi in Florence, and even these and the ribs of the culminating lantern are paired. Thus the entire church, from the ground to the sphere on the lantern, gives the impression of a colossal monolith. At Michelangelo’s death the drum and peristyle of the dome were still under construction. The dome as finally built was heightened somewhat from Michelangelo’s original design, but the effect of the building, seen from the sides or back, follows his original intentions.