Michelangelo, more than any of the many architects who worked on St. Peter's during its construction, is responsible for the success of its design. Fortunately, the building of St. Peter's was generously funded during the 18-year period (1546-64) of his supervision, which took place over the tenures of five popes. Much of the church's revenue during this era came from the Spanish conquest of America.
All aspects of Michelangelo's design served his main goal of preserving Bramante's Greek-cross plan and emphasizing the dome by unifying the design so that the eye is led up to it. Because of later additions to the building's front, the best view of Michelangelo's work is from the papal gardens.
St. Peter's was begun under Bramante in 1506 for Pope Julius II. The first phase of construction is discussed on a page under Bramante.
Between the death of Raphael in 1520 and the appointment of Michelangelo in 1546, work progressed sporadically in accordance with papal initiative and political circumstances.
1520: Appointment of Antonio da Sangallo. After the death of Raphael, Antonio da Sangallo the Younger, who had built the centering under Bramante and served as construction supervisor under Raphael, was made architect-in-chief. He was assisted by Baldassare Peruzzi.
1522-23: Papacy of Hadrian VI. Following the death of Leo X, who had done much to advance the building of St. Peter's, the papal crown passed to Hadrian VI, who had no interest in art and suspended work on this and other Vatican projects.
1523: Accession of Clement VII. After Pope Hadrian's death, Leo X's cousin Giulio de' Medici became Clement VII (1523-34). He made ample funds available for continuing construction, and the south transept arm was begun.
1527: Sack of Rome. Construction ceased after the Sack of Rome, but by the early 1530s, Antonio da Sangallo and Baldassare Peruzzi were again involved with the project.
1534-46: Revision by Antonio da Sangallo. Paul III (1534-49), who succeeded Clement VII, called for a resumption of work on the abandoned site. The pope asked Antonio da Sangallo to prepare a model, which was built between 1539 and 1546. Parts of Antonio's expanded design were built during this period.
1546-64: Revision by Michelangelo. Following the death of Antonio da Sangallo, the position was given to Michelangelo, who reached an agreement with the Fabbrica (board of works) giving him much authority over the design of St. Peter's. Under Michelangelo the drum was nearly completed and much of the south arm and part of the north arm were finished.
1564-66: Appointment of Pirro Ligorio. Pirro Ligorio, who was already in charge of construction at the Belvedere Court of the Vatican Palace, was appointed head architect of St. Peter's by Pius IV. He is thought to have completed the entablature of the drum and built part of the attic story. According to Vasari, Ligorio was relieved of authority at St. Peter's by the next pope, Pius V, because he intended to change Michelangelo's design.
1569: Publication of Dupérac's illustrations. In 1567, the French engraver Étienne Dupérac published a plan, a section, and an elevation that supposedly represented Michelangelo's final design for St. Peter's.
1574: Appointment of Giacomo della Porta. Giacomo della Porta worked on St. Peter's for three decades. He built a number of the remaining parts and nearly brought it to a state of completion.
1580-83: Choir. Bramante's original construction of the choir, which had been built on the foundations begun for the mid- fifteenth-century expansion designed by Bernardo Rossellino for Pope Nicholas V, was replaced with a larger version that matched the transept arms.
Before 1585: North subsidiary dome. The north subsidiary dome over the Gregorian Chapel was built.
1590-93: Lantern. The lantern was constructed.
After 1593: South subsidiary dome. The south subsidiary dome was added over the Clementine Chapel.
1598: Decoration of dome. The decoration of the dome's interior was begun.
When Michelangelo took charge of the project, Antonio da Sangallo had worked on it on and off for 26 years and had radically altered its design. As illustrated by the model, Antonio's overly complex design lacks a focal point.
The treatment of the façade as a separate building connected by loggias gives it a very disjointed and sprawling appearance from the side.
Entrance towers with steeples, another typically Medieval feature, were to have been used at each end of the façade. Because of their height and multi-story complexity, such towers would have drawn attention from the dome.
Antonio's plan is a larger, more complex version of the revised designs by Bramante and Raphael, which reflects Pope Leo X's desire to enlarge the perimeter and add a nave. The augmentation was to be achieved by adding ambulatories outside the apses, which would have weakened the emphasis on the dome.
The walls were articulated as several stories by superimposed orders, which intensified the building's look of clutter and detracted from the dome.
Antonio's dome was to have had an oversized lantern that would have appeared to flatten the solid-masonry dome against the tall, two-stage drum. (The dome of the U. S Capitol building also has a two-stage drum, but its proportions are far different.)
Michelangelo had long been critical of Antonio's plan and model, and in a letter he wrote to one of the members of the Fabbrica, he criticized a number of aspects of Antonio's design. Michelangelo called it "Gothic" and stated that he who departed from Bramante parted from the truth.
|●||Ambulatories. Michelangelo objected to the ambulatories that encircled the apse-ended arms because they prevented light from entering the church and served no meaningful purpose.|
|●||Complexity. Michelangelo complained that Antonio's design was impractical, whereas the first scheme by Bramante was clear and neat.|
|●||Longitudinal plan. Michelangelo argued for the reinstatement of a centralized plan based on a Greek cross with apsidal ends.|
|●||Hiding places. Michelangelo pointed out that Antonio's complex plan provided many cavities wherein crime could be committed and that the process of clearing them at night would entail many guards.|
|●||Demolition of parts of the palace. Michelangelo protested that parts of the Vatican Palace including the Pauline Chapel and perhaps a portion of the Sistine Chapel would have to be cleared to make way for Antonio's outwardly expanded plan.|
Michelangelo made it clear that he would not take on the project unless he could alter Antonio's work and return to Bramante's original Greek-cross plan. He added that because he was in poor health, he was not eager to take on such a task.
The Fabbrica accepted Michelangelo's conditions, and Michelangelo accepted no salary from them, which enhanced his position of authority over the project.
Michelangelo demolished Antonio's ambulatory construction in the south arm, shortened the arms, and eliminated plans for a nave and towers. All that remained of Antonio's work was the partial vaulting of the arms and the raising of the floor level by over nine feet, which eliminated most of the height of the ten-foot-high pedestals that Bramante had planned for the pilasters.
Michelangelo retained Bramante's design for a Greek-cross plan with a dome similar in size to that of the Pantheon, but he made several changes that increased the building's unity and emphasized its dome.
Michelangelo eliminated two exterior features from the perimeter, the four corner towers and the eight galleries.
|=||Elimination of towers. Michelangelo eliminated the corner towers so that there would be no projections along the perimeter to draw the eye out to the corners and away from the dome.|
|=||Elimination of exterior loggias. Without the projections of the corner towers, the recesses containing the exterior loggias no longer existed, and the loggias were eliminated.|
Michelangelo simplified the interior spaces at the corners by replacing the column screens and Greek cross shapes designed by Bramante with circular chapels that opened on two sides so that they form the corners of a square ambulatory just beyond the crossing.
The support that would have been provided by the columns and piers of Bramante's design was compensated for by making the crossing piers larger and the outer walls thicker.
Michelangelo changed Bramante's design of the drum and dome.
|●||Drum. Michelangelo replaced Bramante's series of single columns standing as a screen in front of the windows of the drum with pairs of columns standing between the windows.|
|●||Dome. Michelangelo altered the design of the dome from the horizontally articulated, solid masonry version planned by Bramante to a vertically articulated, double-shelled version, which had a more upward-reaching, graceful appearance. (Michelangelo struggled with the design of the dome and revised its form a number of times. He had planned to retain the hemispherical shape used by Bramante, but a steeper dome was built after his death.)|
The dome, clearly the building's dominant feature, rises high above the rest of the building. Four subsidiary domes, were planned to rise from the four corners, but only the front two were built. Being of a height between the top of the main dome and the attic, they fill in some of the gap between the outer walls and the central dome.
From the exterior, the building's many vaults are hidden behind an attic that unifies the height of the building, creating a continuous border that runs the perimeter of the structure.
On the exterior, the cross-over-square plan is less apparent because Michelangelo angled the walls that connected the hemicycles of the cross to the sides of the square. This increases the building's central mass and the circularity of its shape.
The angling of the corners also increases the number of separate planes.
On both the interior and the exterior, the articulation of the highly sculptural walls is complex enough to avoid monotony over such an extensive expanse yet simple enough to be readily perceived.
The edges of piers form an extra plane between the pilasters and sections of wall, producing a ripple of edges on the exterior. This adds plasticity to the wall surfaces while accentuating their verticality and leading the eye upward toward the dome.
Pilasters and columns are used in pairs, which has several effects.
|=||Unification of levels. The pairing of the pilasters is a repeatable motif that is re-used on the drum and the lantern to unify the different levels. Breaks in the attic story continue the projections of the pilastered zone. Grooves in the ribs of the dome give them a paired look as well.|
|=||Creation of differently sized bays. Using the pilasters in pairs creates two sizes of bays: large bays stand between the pairs of pilasters, and small bays stand between the pilasters of each pair.|
|=||Elastic rhythm. The rhythmic variation created by the use of pairs of projecting verticals and differently sized bays gives the walls a more dynamic appearance and establishes an elastic rhythm that unifies the perimeter shape by leading the eye from plane to plane.|
When Michelangelo died, the attic story had only been completed on the south apse, which is known from contemporary drawings to have been plainer than it is now. Michelangelo is generally thought to have made the attic more decorative in a final design, which is believed to have been represented by a couple contemporary drawings, including Dupérac's elevation, which was published in 1569.
Related to the issue of whether or not the attic as built reflects a final design by Michelangelo is the matter of the role in its design of Pirro Ligorio, who was appointed head architect at St. Peter's by Pius IV after Michelangelo's death. According to Giorgio Vasari, Pius V relieved Pirro Ligorio as chief architect at St. Peter's and other Vatican projects because he intended to alter Michelangelo's design. Vasari did not state where the change was to be made, however.
The temple-front entrance designed by Michelangelo maintained continuity with the rest of the building through the use of columns of the same height and order as the pilasters. The columns were used in a front line of four carrying a pediment and a second line of ten extending to the outer corners. They differed from the pilasters in being evenly spaced.
Unity between the interior and the exterior is achieved by several means.
|=||Wall articulation. The walls of both the interior and exterior are articulated by pairs of Corinthian-order pilasters that define large and small bays.|
|=||Spatial continuity. The impression on the interior of a single space interrupted only by the crossing piers is achieved by Michelangelo's elimination of partitions within the corners. On the outside the effect of a single space within is fostered by an attic that hides the individual roofs of the different vaults. The use of angled corners also creates spatial continuity by minimizing the building's resemblance to a cross overlaid by a square.|
Pairs of Corinthian columns stand in front of a series of piers that support the ribs of the dome.
Use of columns in pairs on the drum and lantern links them visually to the pairs of pilasters on the lower walls as if they are part of a single supportive framework although structurally, they are unconnected because the drum is supported by pendentives rising from the crossing piers.
Pilasters decorate the corners of the piers.
As illustrated by the model, Michelangelo had intended to place sculpted figures on the giant scrolls on the ledge above the entablature.
From the time he was appointed chief architect, Michelangelo considered the design of the dome of St. Peter's, and in 1547, he sent to Florence for the construction drawings and vertical measurements of Brunelleschi's dome of Florence Cathedral, the largest dome built since antiquity. Like his Florentine predecessor, Michelangelo designed a dome constructed of two brick shells that were connected by vertical ribs. His dome differed from Brunelleschi's dome in having sixteen ribs instead of twenty-four and in exposing all of them instead of only every third one. Both domes are among the largest structures in the history of architecture.
Giacomo della Porta built both the main and subsidiary domes. Working around two and a half decades after Michelangelo's death, Giacomo generally followed Michelangelo's design, but he built the dome steeper than hemispherical. He also created narrower ribs and supports and eliminated the taper at the top, which would have made it appear to be further from the viewer, and therefore, taller.
It is not known whether the decision to build it steeper was an aesthetic or practical decision. Brunelleschi would have preferred to build a hemispherical dome at Florence Cathedral, but he was forced by the limitations of the existing drum to build a steeper version because it would exert less lateral thrust. Michelangelo himself had considered a steeper dome at one point, and the additional height is in no way incompatible with the rest of his design.
The ceiling of the dome, which was not finished until 1612, was decorated according to Baroque taste.
The dome, including its drum and lantern, is the most admired feature of St. Peter's. Architects in later centuries studied it, and some degree of influence is evident in the domes of many famous churches and other public buildings.
The lantern was built according to Michelangelo's design except that its base is shorter.
Michelangelo's lantern features a ring of paired columns carrying an entablature. Scroll-faced triangular buttresses brace both the lantern's attic and its base.
The concave curve of the roof, which provides a counter-curve to the dome's convex shape, sweeps the eye up to the top. An orb (sphere) and a cross, which together symbolize monarchical power and justice, rise from the top.
Because Michelangelo left no designs for the subsidiary domes and those illustrated by Dupérac are more in accord with the style of his successor, Vignola, there is some question as to whether he changed his mind about including them.
The existing front subsidiary domes were designed and built by Giacomo della Porta. The north subsidiary dome was constructed before the dome itself.
In the next century, the focus of the church was moved toward its entrance end, and the back two domes were not constructed. Although they would have given the west end greater unity, the rear subsidiary domes were no longer needed to maintain the symmetry of the whole building, which was now axial instead of radial.
In the seventeenth century, St. Peter's was expanded by several major additions to the building, its interior, and its forecourt. The addition of three nave bays and a wide façade block a view of the dome from the front.
On the order of Pope Paul V (1607-14), a three-bay nave was added to St. Peter's by Carlo Maderno, an early-Baroque architect. The nave ceiling was a tunnel vault formed by extending the east vault of the crossing.
Maderno also designed the entrance façade, which was to include a pair of towers, but these were not built due to the weakness of the façade's foundation. The façade resembles Michelangelo's design only in its use of a temple-front with Corinthian columns of the same height as the pilasters.
The design of the façade was affected by the inclusion of a new Benediction Loggia to replace the old Benediction Loggia, which had been attached to the front of the atrium of Old St. Peter's. Because a recessed porch like the one Michelangelo designed would have left the papal balcony in the shadows, the balcony was projected outward, which made the pope visible to the crowds that gathered to receive his benediction.
The original twisted columns were incorporated into the niches on the inner facings of the crossing piers.
The Cathedra Petri, the throne of St. Peter, which has now been identified as dating from the ninth century, is displayed by an ensemble of sculpture and architecture.
The polychrome quality of the seventeenth-century sheathing of marble detracts from the sculptural quality of the interior architecture by obscuring the perception of its planes, contours, and edges.
To make the church accessible from all sides like a work of sculpture, Michelangelo had planned for the church to be freestanding on a piazza, though he could not have envisioned one so wide as this illustration shows because of the proximity of the Vatican Palace.
In 1586 Pope Sixtus V commissioned Domenico Fontana to move the obelisk that then stood south of St. Peter's. In ancient Roman times, this obelisk had been brought from Egypt and mounted in the center of Nero's hippodrome.
Using 800 men, 140 horses, and 40 crank winches, Fontana moved the obelisk to its current position, which was then outside the old entrance to the Vatican. This obelisk was the first and largest of several obelisks that Pope Sixtus commissioned Fontana to move.
Although the fountains were designed as a symmetrically placed pair, they were made and erected at different times. The fountain on the north side was made by Carlo Maderno, who signed the contract in 1614. Maderno's fountain was erected later by Bernini, who built and installed a matching fountain on the south side.
In place of the atrium of Old St. Peter's, which had become a hodgepodge of appended buildings, Bernini created an enclosed piazza that was formed by long two-part wings that extend forward from each side of the façade like embracing arms.
The two-part arms consist of straight sections that define a trapezoid next to the façade and curved sections that define an ellipse next to the trapezoid.
Together the trapezoid and the ellipse form a keyhole shape in plan, giving the piazza's shape a thematic linkage to St. Peter, to whom Christ gave the keys of the Kingdom. Keys are part of the papal arms.
Bernini's creation of a trapezoidal space whose wide end stood next to the Church's façade magnified the viewer's perception of the building's size.
Bernini designed the part of the piazza opposite St. Peter's to be closed by a short section of colonnade. Had his design been executed, it would have prevented a clear view of the piazza from beyond and allowed visitors entering the piazza to enjoy the thrill of suddenly discovering a vast expanse enclosed by a nearly continuous elliptical colonnade.
A rectangular area whose width equaled that of the opening between the colonnade arms was opened up at the entrance to the piazza. When seen from St. Peter's, the piazza no longer terminated with an ellipse.
Various schemes for improving the approach to St. Peter's have been proposed over the years.
In the late 1930s, the Piacentini-Spaccarelli plan was enacted under Mussolini, and the buildings along the central axis, the Spina del Borgo were removed. A frontal view of St. Peter's can now be seen from many blocks away along the street leading from the Castel Sant'Angelo.
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