The Basilica of St. Peter is the largest Catholic church in the world. The construction of the building began in 1506, under Pope Julius II, and ended in 1626, under Pope Urban VIII. It stands on the early Christian Basilica of Constantine I (fourth century), built on the tomb of St. Peter. It was Pope Julius II to entrust the renovation project to Bramante, who developed a crucial idea for the Renaissance architecture: a central plan, covered by a large dome inspired by the Pantheon. Bramante was followed bybRaphael, Antonio da Sangallo and Baldassarre Peruzzi. In 1538, Antonio da Sangallo the Younger proposed a synthesis between the various projects: a domed front building, flanked by two tall bell towers. To Sangallo succeeded Michelangelo Buonarroti, who returned to the original central plan, adding a porch. Until the completion, the works were followed by Giacomo Della Porta (smaller domes) and Carlo Maderno: Latin cross with three naves, with deep chapels placed along the perimeter walls, facade with columns of giant order and steeples on the sides. In the definition of the ornamental apparatus was instrumental Gian Lorenzo Bernini, who worked to the octagon under the dome and to the coating, as well as the grand design of St. Peter's Square: a scenic route that takes the audience from narrow streets to the Square and Basilica, making the dome the prominent element. The interior, which is accessible through five monumental gates (works of Manzu, Minguzzi, Filarete, Crocetti and Consorti), is divided into 11 chapels and has a total of 45 altars: in the first chapel on the right there is the famous "Pietà" by Michelangelo (1499); follows the Chapel of St. Sebastian, of the Blessed Sacrament (with a deleted by Borromini and a Bernini's tabernacle); on the left, the Chapel of Baptism (designed by Carlo Fontana and decorated with mosaics) and the Chorus. At the altar of St. Jerome, on the right aisle, is the tomb of Pope John XXIII; follows the altar of the Sacred Heart of Jesus, the Chapel of the Virgin of the Pillar and the eighteenth-century altar of St. Peter healing a paralytic. The space under the dome is marked by monumental canopy of St. Peter, by Gian Lorenzo Bernini: 30 meters high and supported by four twisted columns in imitation of the Temple of Solomon. The so-called "Vatican Grottoes", formed in the gap between the new and the old Basilica, have the form of an underground church with three naves and act as the burial place of many pontiffs.