Designed principally by Donato Bramante, Michelangelo, Carlo Maderno and Gian Lorenzo Bernini, St. Peter's is the most renowned work of Renaissance architecture and remains one of the largest churches in the world. While it is neither the mother church of the Catholic Church nor the Catholic Roman Rite cathedral of the Diocese of Rome, St. Peter's is regarded as one of the holiest Catholic sites. It has been described as "holding a unique position in the Christian world" and as "the greatest of all churches of Christendom".
By Catholic tradition, the basilica is the burial site of its namesake Saint Peter, one of the twelve apostles of Jesus and, also according to tradition, the first Pope and Bishop of Rome. Tradition and strong historical evidence hold that Saint Peter's tomb is directly below the altar of the basilica. For this reason, many Popes have been interred at St. Peter's since the Early Christian period. There has been a church on this site since the time of the Roman Emperor Constantine the Great. Construction of the present basilica, replacing the Old St. Peter's Basilica of the 4th century AD, began on 18 April 1506 and was completed on 18 November 1626.