St Peter's Basilica facts: the tomb under the altar, 120 years of building, Michelangelo's dome, Bernini's square, the numbers and the myths

Architecture · 4 September 2026

St Peter's Basilica in Vatican City is the largest church in the world, 220 m long, with a dome 136 m high, built between 1506 and 1626 over the grave of the apostle Peter, who was crucified in Nero's circus on the Vatican hill about AD 64 and buried in a cemetery beside it; the first basilica was built over the grave by Constantine from about 320, stood for 1,200 years, and was pulled down to make way for the present church, designed in turn by Bramante, Raphael, Antonio da Sangallo, Michelangelo, who gave it the dome, Carlo Maderno, who added the nave and facade, and Bernini, who made the baldachin and the square. It was paid for partly by the sale of indulgences that provoked Martin Luther in 1517. It is not a cathedral, the pope's cathedral being St John Lateran, but the church of the papacy's great ceremonies and of some 91 papal tombs. Below: the grave, the two churches, the architects, the dome, the works of art, the square, the numbers, visiting, and the myths, with the church in the Buildings by style collection and its style in Renaissance architecture and Baroque architecture.

The grave of Peter

The tradition, recorded by the Roman presbyter Gaius about AD 200, placed Peter's "trophy" on the Vatican hill, and Constantine's basilica was built with its altar over a small shrine there, cutting into the hill and the cemetery around it at great cost to do so. Between 1940 and 1949 Pius XII had the ground under the altar excavated, and the archaeologists found a Roman street of mausoleums of the 2nd century, and under the altar a niche monument of about AD 160 against a red-plastered wall, with graffiti invoking Peter and, in a marble-lined cavity in a side wall, bones wrapped in purple and gold cloth. The bones were studied in the 1960s by Margherita Guarducci, who identified them as a man of sixty to seventy, and in 1968 Paul VI announced them as Peter's "in a manner we believe convincing"; the identification is accepted by the Church and treated as probable but unproven by most historians. The shrine is directly below the papal altar and the dome, and can be seen on the Scavi tour, limited to a few hundred people a day. St Peter's Basilica.

Old St Peter's, 320–1506

Constantine's church was a five-aisled basilica about 110 m long, with a transept in front of the shrine and an atrium with a fountain, roofed in timber, floored with the mosaics of the cemetery it stood on; Charlemagne was crowned emperor in it on Christmas Day 800, and it received the pilgrims of Europe for 1,200 years. By the 15th century its walls leaned 1.5 m out of true and Nicholas V began a new choir in 1452 that was abandoned at his death; in 1505 Julius II, wanting a setting for the tomb Michelangelo was to carve him, decided to demolish and rebuild, and Bramante's design won. The demolition of the old church, its mosaics, tombs and altars, was the scandal of the age, and Bramante was called "Maestro Ruinante"; a few things survived, including the bronze pine cone of the atrium, now in the Vatican museums, the Navicella mosaic of Giotto, and the tomb slabs in the grottoes.

The new basilica, 1506–1626

• Bramante, 1506–14. The first stone on 18 April 1506. A Greek cross of four equal arms under a dome the size of the Pantheon's, "the Pantheon raised on the Basilica of Maxentius"; the four great piers of the crossing are his, and they proved too weak and had to be reinforced.
• Raphael, Peruzzi, Sangallo, 1514–46. Raphael turned the plan into a Latin cross with a nave; Peruzzi turned it back; Antonio da Sangallo made a wooden model 7 m long, still in the Vatican, of a version with towers and a nave, and strengthened the piers.
• Michelangelo, 1547–64. Appointed at 71, unpaid, "for the love of God", he swept away Sangallo's plan, returned to Bramante's Greek cross, thickened the walls and piers, designed the apses of the exterior with their giant Corinthian pilasters, and the dome, whose drum was finished when he died in 1564; the dome was built to his model by Giacomo della Porta and Domenico Fontana in 1588–90, made a little taller and more pointed than Michelangelo's hemisphere.
• Maderno, 1607–15. Paul V decided the church must cover the whole area of the old one and hold larger crowds, and Maderno extended the nave by three bays to make a Latin cross and built the facade, 115 m wide and 45 m high, which hides the dome from the square and is the part of the building everyone criticises.
• Bernini, 1624–67. The bronze baldachin over the altar, 29 m high, cast from bronze stripped from the Pantheon's porch, the Chair of Peter in the apse, the tombs of Urban VIII and Alexander VII, the equestrian Constantine, and the square with its colonnade. Consecration on 18 November 1626, 1,300 years after Constantine's; the bell towers Bernini added to the facade cracked it and were demolished.

The indulgences and the Reformation

The building cost more than the papacy had, and in 1507 Julius II, and in 1515 Leo X, offered a plenary indulgence, the remission of the punishment due for sins, to those who gave money for St Peter's. In Germany the Dominican Johann Tetzel sold it with the jingle "as soon as the coin in the coffer rings, the soul from purgatory springs", half the proceeds going to the archbishop of Mainz to repay the bankers who had bought him his office. On 31 October 1517 Martin Luther posted his Ninety-five Theses against the sale, asking why the pope, richer than Crassus, did not build St Peter's with his own money rather than the poor's. The building therefore stands at the start of the Reformation, and the Council of Trent, which answered Luther, was still sitting when Michelangelo took over the dome. Money later came from the papal states, from Spain and its silver, and from the Jubilees.

The dome

Michelangelo's dome is a double shell of brick, 42 m across inside, one metre less than the Pantheon's, rising to 136.6 m at the top of the cross, on a drum ringed by paired columns; the inner shell is the ceiling seen from the church, the outer the ribbed dome seen from the city, with a stair between them that visitors climb. The drum carries the weight of 14,000 tons on Bramante's four piers, and the dome pushes outward, so it was built with iron chains embedded in the masonry, and when it cracked in the 1740s the mathematicians of Benedict XIV, the "three mathematicians" led by Boscovich, and the engineer Poleni added five more chains, still there. Della Porta raised Michelangelo's profile by about 7 m for strength and the look from the ground. The mosaic inscription around the base of the drum, "Tu es Petrus", is in letters 2 m high. Michelangelo's model in limewood survives in the Vatican, and the dome became the pattern for St Paul's in London, the Panthéon in Paris, the Capitol in Washington and St Isaac's in St Petersburg.

What is inside

• The Pietà. Michelangelo's marble of 1498–99, made when he was 24, the only work he signed, on the Virgin's sash after hearing it attributed to someone else; behind glass since a man attacked it with a hammer in 1972.
• The baldachin. Bernini's bronze canopy on twisted columns over the papal altar, above the grave; the twisted form copies columns from Constantine's church said to have come from Solomon's Temple, eight of which are in the piers around it.
• The statue of Peter. A bronze seated figure, attributed to Arnolfo di Cambio around 1300, whose right foot has been worn smooth by the kisses and touches of pilgrims.
• The Chair of Peter. Bernini's gilt bronze throne of 1666 in the apse, enclosing a wooden chair given to the pope by Charles the Bald in 875, below a window of the Holy Spirit in yellow alabaster.
• The tombs. Ninety-one popes in the church and the grottoes below, with monuments by Bernini, Canova (Clement XIII), Pollaiuolo (Sixtus IV and Innocent VIII, brought from the old church) and the tomb of Queen Christina of Sweden and of the last Stuarts; John Paul II lies in the chapel of St Sebastian.
• The mosaics. Almost every "painting" in the church is a mosaic copy, made in the Vatican workshop from the 17th century because canvases and frescoes rotted in the damp; the altarpieces of Raphael, Domenichino and Guercino are in the Vatican museums.
• The floor marks. Brass lines in the nave floor mark the lengths of the world's other great churches, from St Paul's in London at 158 m down, all shorter.

The square and the numbers

Bernini's Piazza San Pietro (1656–67) is an ellipse 240 m across, embraced by two curved colonnades of 284 columns four deep, "the motherly arms of the Church", with 140 statues of saints on top, around the Egyptian obelisk brought to Rome by Caligula in AD 37, which stood in Nero's circus beside Peter's execution and was moved to the centre of the square by Fontana in 1586 with 900 men, 140 horses and 44 winches; two fountains flank it, and two discs in the pavement mark the points from which each colonnade's four rows line up as one. The basilica is 220 m long outside, 187 inside, and 150 m across the transepts; the nave is 46 m high; the floor area is 15,160 square metres, with room for about 60,000 standing; the facade carries 13 statues of Christ, the Baptist and eleven apostles, each 5.7 m; the largest bell weighs 9 tons. About 11 million visitors a year enter, free, through security queues that run to two hours; the dome climb, 551 steps or a lift and 320 steps, costs a few euros. The Vatican City around it, 44 hectares, is the smallest state in the world.

Versions and theories

• Are the bones Peter's? The Church says yes; the archaeology shows a 2nd-century shrine that Christians of Rome believed marked his grave, and bones of a man of the right age moved into the wall near it, possibly by Constantine's builders. Peter's presence in Rome is accepted by most historians; the bones cannot be proved.
• Michelangelo designed the dome as built. Mostly: the drum, the ribs and the double shell are his; della Porta raised the curve. Michelangelo's own drawings show him considering both profiles.
• Bernini stole the bronze from the Pantheon. Urban VIII did, in 1625, stripping the portico's beams; Romans said "what the barbarians did not do, the Barberini did". Most of it went to cannon for the Castel Sant'Angelo and the rest to the baldachin.
• The bell towers cracked the facade. Bernini's south tower of 1641 caused cracks in Maderno's facade, whose foundations were on an old stream, and was demolished in 1646; the facade's proportions are still blamed on the missing towers.
• St Peter's is the largest church on earth. By interior area, yes, 15,160 square metres; the Basilica of Our Lady of Peace at Yamoussoukro in Ivory Coast, built in 1990 as a copy, is taller and claims a larger overall area, but its dome was made lower than St Peter's by agreement.
• The secret passage. The Passetto di Borgo, a covered walkway on top of the wall from the Vatican to the Castel Sant'Angelo, is real and saved Clement VII in the Sack of Rome in 1527; it is open to visitors some summers.

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