Taken March 7th, 2009, St. Peter’s Basilica , The Vatican.
The dome of St. Peter’s was designed by Michelangelo, who became chief architect in 1546. At the time of his death (1564), the dome was finished as far as the drum, the base on which domes sit. The dome was vaulted between 1585 and 1590 by the architect Giacomo della Porta with the assistance of Domenico Fontana, who was probably the best engineer of the day. Fontana built the lantern the following year, and the ball was placed in 1593.
The great double dome is made of brick and is 42.3 metres in interior diameter (almost as large as the Pantheon), rising to 120 metres above the floor. In the early 18th century cracks appeared in the dome, so four iron chains were installed between the two shells to bind it. The four piers of the crossing that support the dome are each 60 feet (18 meters) across.
Uniquely, Michelangelo’s dome is not a hemisphere, but a parabola: it has a vertical thrust, which is made more emphatic by the bold ribbing that springs from the paired Corinthian columns, which appear to be part of the drum, but which stand away from it like buttresses, to absorb the outward thrust of the dome’s weight. Above, the vaulted dome rises to Fontana’s two-stage lantern, capped with a spire.
Surrounding the baldacchino, the canopy over the main altar, are four great piers that support the huge dome. Each pier has a large niche at its base, which is filled with a colossal statue of a saint representing each of the basilica’s four major relics (Reliquae Maggiori):
– NW pier – St Helena, Constantine’s mother, holding a large cross (representing the relic of the True Cross found by the saint in Jerusalem)
– NE pier – St Longinus, the Roman soldier who thrust a spear in the side of Christ at the crucifixion, converted, and was later martyred (the relic is the spear) (statue by Bernini)
– SE pier – St Andrew, with his trademark diagonal cross upon which he was martyred (the relic is Andrew’s head, which was returned to the Greek Orthodox Church in 1964)
– SW pier – St Veronica, with the veil Christ used to wipe his face on the way to Calvary, leaving his image imprinted on it (representing the relic of Veronica’s veil)
The balconies above the niches are flanked by the 4th-century spiral columns of the baldacchino in the Constantinian St. Peter’s, and contain reliefs depicting the relics.
Along the base of the inside of the dome is the inscription of Matthew 16:18-19, in letters 8 ft. (2.5m) high:
TV ES PETRVS ET SVPER HANC PETRAM AEDIFICABO ECCLESIAM MEAM. TIBI DABO CLAVES REGNI CAELORVM (You are Peter, and on this rock I will build my church…. I will give you the keys of the kingdom of heaven.)
Near the top of the dome is another, smaller, circular 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 and the fifth year of his pontificate.)