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 two 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.
St. Peter's is famous as a place of pilgrimage, for its liturgical functions. Because of its location in the Vatican, the Pope presides at a number of services throughout the year, drawing audiences of 15,000 to over 80,000 people, either within the Vatican Basilica, or in St. Peter's Square. St. Peter's has many strong historical associations, with the Early Christian church, the papacy, the Protestant Reformation and Counter-reformation, and with numerous artists, most significantly Michelangelo. As a work of architecture, it is regarded as the greatest building of its age. St. Peter's is one of the four churches of Rome that hold the rank of Major Basilica. Contrary to popular misconception, it is not a cathedral as it is not the seat of a bishop; the cathedra of the Pope (as Bishop of Rome) is located in the Archbasilica of St. John Lateran.