The first St. Peter's, now referred to as Old St. Peter's, was built on the site of Nero's hippodrome just across the Tiber from the city of Rome. By the Renaissance, Old St. Peter's was part of a complex of buildings, which made up the Vatican.
Old St. Peter's contained the tomb of St. Peter, who Jesus entrusted with the founding of the Church. Consequently, it was the most sacred structure of the Roman Catholic Church. In addition, it was built by Constantine, the first Christian emperor, which added to its historic significance.
Built around 330, Old St. Peter's was over eleven and a half centuries old at the beginning of the sixteenth century, and it badly needed to be repaired structurally. None of the popes had taken on this problem, and even the remodeling project begun under Pope Nicholas V by Bernardo Rossellino focused on expansion rather than repair.
Pope Julius II, who became Pope in 1503, was the motivating force in the project to enlarge Old St. Peter's or replace it.
|●||Restoration of Rome's greatness. Pope Julius regarded St. Peter's as an important part of his building program, which was intended to symbolize the restoration of Rome's ancient position of power and prestige. As ruler over much of Christendom, he felt himself to be an heir to both the emperors of the Roman Empire and the papacy of the Roman Catholic Church.|
|●||Desire for Inclusion of own tomb. Julius also wanted to commemorate his own greatness by incorporating his tomb in the addition to Old St. Peter's or its replacement. To this end, in 1506 he commissioned Michelangelo to make him a magnificent three-tier tomb.|
Initially Julius planned to repair the existing structure, but in 1506, he decided to tear it down so that a new one of unprecedented size and splendor could be built on the same site.
To finance this ambitious undertaking, Julius requested that foreign churches send more money to Rome and encouraged the selling of indulgences (forgivenesses). These and other fund-raising policies were contributing factors to the Reformation.
Julius preferred the designs of Bramante, who had been working for him as the chief architect on the Belvedere Court project at the Vatican since 1505, to those of other architects who were consulted such as Giuliano da Sangallo, who had accompanied him on a trip to France in 1495-96 and designed the della Rovere palace in Savona at that time.
Bramante's first design, which was made by 1506, is known from two sources:
A medal to commemorate the laying of the cornerstone of the new St. Peter's was struck in 1506 by Caradosso, a sculptor who had worked on the architectural ornament of some of Bramante's buildings in Milan.
A number of features can be identified from the image on the medal.
On the back of this plan is a notation by Antonio da Sangallo the Younger, who assisted in the construction of the centering, indicating that this is not the version constructed under Bramante.
The parchment plan roughly corresponds to the façade depicted on the medal.
This plan, which has four identical quadrants, is made up of several distinct parts.
Bramante worked on several versions between 1506 and his death in 1514.
After succeeding Pope Julius in 1513, Pope Leo X called for making St. Peter's even larger and grander. He appointed Fra Giocondo and Giuliano da Sangallo to assist Bramante, but when Bramante died a year later, a definitive version had not yet been determined.
Raphael was then made the head architect, and Fra Giocondo and Giuliano da Sangallo assisted him until their deaths in 1515 and 1516, respectively. After the premature death of Raphael in 1520, Antonio da Sangallo the Younger, was appointed to replace him as the chief architect, and Baldassare Peruzzi was appointed to assist him.
The plan linked to Peruzzi may reflect Bramante's latest design, or it may have originated with Raphael or Peruzzi himself. Versions of this plan are known from two sources.
|1.||Peruzzi's drawing. A drawing attributed to Peruzzi illustrates a perspective version of a plan and multiple sections of St. Peter's.|
|2.||Serlio's publication. A woodcut published by Serlio illustrates a plan of St. Peter's that corresponds to Peruzzi's perspective version.|
This plan is similar to Bramante's first plan in having a large Greek cross, four smaller Greek crosses, and four corner towers.
It is different in having dropped the exterior loggias connecting the apses to the corner towers and having added piers and columns to the interior that would form ambulatories in the apses.
A version with a nave by Raphael was also published by Serlio.
Raphael's plan differs from the other versions in having one longer arm containing a nave, side aisles, and chapels. Also, its corner towers, of which there are only two, are smaller and do not project from the wall planes enclosing the small Greek-cross areas.
Like the plans by Bramante and Peruzzi, Raphael's plan includes apsidal ambulatories and small Greek crosses, but due to the nave occupying one side, there were only three apsidal ambulatories and only two small Greek crosses.
Bramante determined the dimensions of New St. Peter's from those of Old St. Peter's. From its nave, he set the distance between the sides of the crossing piers. The dome, whose size is a factor of this spacing, is as wide as the nave and inner aisles combined.
Although the plan was changed and expanded by Michelangelo and others, the setting of the crossing piers forever determined the diameter of the dome and the width of the cross arms, which were coffered barrel vaults. Similarly, the height of the crossing arches forever established the height of the nave.
There is nothing to suggest that the original design of the dome would have been affected by the revisions to the plan.
According to these illustrations, Bramante had planned a hemispherical dome like that of the Pantheon.
Instead of using double-shell construction like Brunelleschi had employed to lighten the dome of Florence Cathedral, which was similar in size, Bramante planned a single-shell dome of cemented masonry.
Bramante's dome would have rested on a colonnaded drum, which would have been the first of its type. Bramante had used columns on his earlier dome for Santa Maria delle Grazie, but they had been part of an arcade rather than a colonnade.
Bramante's use of the post-Roman invention of pendentives to support the dome distinguishes it from the Pantheon, whose dome rests on a circular wall that corresponds to the drum of Renaissance domes.
The diameter of the dome of St. Peter's was greater than the distance between the sides of the crossing piers. This represented a bold departure from the pendentive-based domes used in Florence in the fifteenth century.
Domes that were wider than their naves had precedent in late-medieval Italian cathedrals whose domes were supported by more than four piers. Florence Cathedral had eight piers, and Siena Cathedral had six.
Some fifteenth-century Roman churches like Santa Maria della Pace also followed this wide-rotunda, multi-pier type.
The dome Bramante designed for the enlargement of the east end of Santa Maria delle Grazie in Milan is also wider than the nave. Its piers are not free-standing, but instead, are part of the exterior walls.
By changing the shape of the crossing piers from being essentially square in section to being essentially triangular in section, Bramante was able to achieve a four-pier dome that was wider than the nave.
This form was achieved by chamfering, or beveling, the inner corners of traditional square piers so that diagonal planes faced the center. Equivalent support was achieved through an increase in the widths of the piers.
Bramante designed ten-foot high platform bases to carry the pilasters, which meant that the pilaster bases would have been above eye level if the floor level had not been raised in a later building phase.
The projection of the trim and the recession of the niches gives a sculptural quality to the crossing piers.
The completed portion at the time of Bramante's death consisted of the four crossing piers (including their articulation by pilasters), the four crossing arches that they supported, parts of other piers, and part of the sanctuary arm.
Building on the scale of the Roman baths was outside of the experience of Renaissance architects like Bramante, who could not know for sure how large to make the piers.
The piers, which Serlio reported to have been cracking before they were finished, later had to be expanded to withstand the weight of the dome.
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