San Pietro - (St Peter's Basilica)
The Basilica of Saint Peter , officially known in Italian as the Basilica di San Pietro in Vaticano and commonly called Saint Peter's Basilica , is one of four major basilicas of Rome ( St. John Lateran , St. Peter's, Santa Maria Maggiore and St. Paul outside the Walls ). It is the most prominent building inside the Vatican City and built on the ruins of Old Saint Peter's Basilica . Its dome is also a dominant feature of the Roman skyline. Saint Peter's is also incidentally the patriarchal basilica of Constantinople, whereas the Lateran Basilica is the patriarchal basilica of Rome. Possibly the largest church building in Christianity , it covers an area of 5.7 acres (2.3 ha ) and has a capacity of over 60,000 people. One of the holiest sites of Christendom in the Catholic tradition, it is traditionally the burial site of its namesake Saint Peter , who was one of the twelve apostles of Jesus . According to Catholic tradition, also the first Bishop of Antioch , and later first Bishop of Rome . Although the New Testament does not mention Peter's presence or martyrdom in Rome, Catholic tradition holds that his tomb is below the baldachin and altar ; for this reason, many Popes , starting with the first ones, have been buried there. Construction on the current basilica, over the old Constantinian basilica, began on April 18 , 1506 and was completed in 1626. Although the Vatican basilica is not the Pope's official seat ( Saint John Lateran ), it is most certainly his principal church, as most Papal ceremonies take place at St. Peter's due to its size, proximity to the Papal residence, and location within the Vatican City walls. The basilica also holds a relic of the Cathedra Petri , which is, according to Catholic tradition, the episcopal throne of the basilica's namesake when he supposedly led the Roman church, but which is no longer used as the Papal cathedra . It is believed that a piece of this cathedra, or chair, is contained within the altarpiece, designed by Bernini .