The Papal Basilica of Saint Peter (officially known in Italian as the Basilica Papale di San Pietro in Vaticano and commonly known as St. Peter's Basilica) is located within the Vatican City. St. Peter's Basilica has the largest interior of any Christian church in the world, holding 60,000 people. It is the symbolic "Mother church" of the Catholic Church and is regarded as one of the holiest Christian sites. It has been described as "holding a unique position in the Christian world" and as "the greatest of all churches of Christendom". In Catholic tradition, it is the burial site of its namesake Saint Peter, who was one of the twelve apostles of Jesus and, according to tradition, first Bishop of Rome and therefore first in the line of the papal succession.
Tradition and some 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 4th century. Construction of the present basilica, over the old Constantinian basilica, began on April 18, 1506 and was completed on November 18, 1626.