After 120 years as a building site, the current St Peter's was consecrated on 18 November 1626 by Urban VIII - exactly 1,300 years after the consecration of the first basilica on the site.
The earlier building was a five-aisled classical basilica, fronted by a large courtyard and four porticoes. Enlarged and enriched, it became the finest church in Christendom. By the mid 15th century, however, its south wall was collapsing. Pope Nicholas V had 2,500 wagonloads of masonry from the Colosseum carted across the Tiber, just for running repairs. No one wanted to take responsibility for demolishing Christianity's most sacred church. It took the arrogance of Pope Julius II and his pet architect Donato Bramante to get things moving. In 1506 some 2,500 workers tore down the 1,000-year-old basilica, and Julius laid the foundation stone for its replacement.
Following Bramante's death in 1514, Raphael took over the work and scrapped his predecessor's design for a basilica with a Greek-cross plan, opting for an elongated Latin cross. In 1547 Michelangelo took command and reverted to a Greek cross. He died in 1564, aged 87, but not before coming up with a plan for a massive dome and supporting drum. This was completed in 1590, the largest brick dome ever constructed, and still the tallest point of any building in Rome. In 1607 Carlo Maderno won the consent of Pope Paul V to demolish the remaining fragments of the old basilica and put up a new façade, crowned by enormous statues of Christ and the apostles.
After Maderno's death Bernini took over and, despite nearly destroying both the façade and his reputation by erecting towers on either end (one of which fell down), he became the hero of the hour with his sumptuous baldacchino and elliptical piazza. This latter was built between 1656 and 1667, its colonnaded arms reaching out towards the Catholic world in a symbolic embrace. The oval measures 340 by 240 metres (1,115 by 787 feet), and is punctuated by the central Egyptian obelisk (erected by a workforce of 800 in 1586) and two symmetrical fountains by Maderno and Bernini. The 284-column, 88-pillar colonnade is topped by 140 statues of saints.
In the portico (1612), opposite the main portal, is a mosaic by Giotto (c1298) from the original basilica. Five doors lead into the basilica: the central ones come from the earlier church, while the others are all 20th-century. The last door on the right is opened only in Holy Years by the pope himself (and, as seen from the inside, is firmly cemented shut).
Inside, the basilica's size is emphasised on the marble floor, where a boastful series of brass lines measure the lengths of other churches around the world that haven't made the grade (second longest is St Paul's, London). But it is Bernini's vast baldacchino (1633), hovering over the high altar, which is the real focal point. Cast from bronze purloined from the Pantheon by Bernini's patron, Pope Urban VIII, of the Barberini family, it prompted local wits to quip 'quod non fecerunt barbari, fecerunt Barberini' ('what the barbarians didn't do, the Barberini did').
An extraordinary piece of Baroque design, it takes its form from a Mesopotamian tradition in which woven silken cloth was draped over a framework to mark a sacred spot. In Bernini's hands it became a hundred feet of gilded bronze. The canopy stands over the high altar officially reserved for the Pope; below, two flights of stairs lead beneath the altar to the confessio, where a niche contains a ninth-century mosaic of Christ, the only thing from old St Peter's that stayed in the same place when the new church was built. Far below lies the site of what is believed to be St Peter's tomb, discovered during excavations in 1951.
Pilgrims head straight for the last pilaster on the right before the main altar, to kiss the big toe of Arnolfo da Cambio's brass statue of St Peter (c1296), worn down by centuries of pious lips, or to say a prayer before the crystal casket containing the mummified remains of much-loved Pope John XXIII, who was beatified in 2002. Tourists, on the other hand, make a beeline for the first chapel on the right, where Michelangelo's first major work, the Pietà (1499), is found. He signed his name on the thin sash across the Virgin's chest in response to cynics who claimed that he was too young at 25 to have produced the piece himself. The statue's position behind bullet-proof glass means the signature is only visible with strong binoculars or on postcards. Proceeding around the basilica in an anti-clockwise direction, notice Carlo Fontana's highly flattering monument to the unprepossessing Queen Christina of Sweden, a convert to Catholicism in 1655, to the left of the Pietà chapel. The third chapel has a tabernacle and two angels by Bernini, plus St Peter's only remaining painting: a Trinity by Pietro da Cortona (the others have been replaced by mosaic copies). In the first chapel beyond the right transept is a tear-jerker of a neo-classical tomb (1792), the last resting place of Pope Clement XIII, by Antonio Canova.
Bernini's Throne of St Peter (1665), flanked by papal tombs, stands at the far end of the nave beyond the high altar, under a stained-glass window. Encased within Bernini's creation is a wood and ivory chair, probably dating from the ninth century but for many years believed to have belonged to Peter himself. To the right of the throne is Bernini's 1644 monument to his patron Urban VIII, who commissioned the bronze portrait (between statues of Charity and Justice) before his death. On the pillars supporting the main dome are much-venerated relics, including a chip off the True Cross above the statue of St Helena bearing the cross she is said to have brought back from the Holy Land.
In the left aisle, beyond the pilaster with St Veronica holding the cloth with which she wiped Christ's face, Bernini's tomb for Pope Alexander VII (another of his patrons) shows the pope seated above a doorway shrouded with a cloth of reddish marble, from beneath which struggles a skeleton clutching an hour-glass: a grim reminder of the fleeting nature of life.
Near the portico end of the left aisle is a group of monuments to the Old Pretender James Edward Stuart (the 18th-century claimant to the throne of England and Scotland, and here recorded as King James III), his wife Maria Clementina Sobieski and their sons Charles Edward (Bonnie Prince Charlie) and Henry Benedict. They are buried in the grottoes below.
Beneath the basilica are the Vatican Grottoes - Renaissance crypts containing papal tombs. The Necropolis, where St Peter is said to be buried, lies under the grottoes. The small treasury museum off the left nave of the basilica contains some stunning liturgical relics. The dome, reached via hundreds of stairs (there's a cramped lift as far as the basilica roof), offers fabulous views of the Vatican gardens.