St. Peter 's Basilica , which is called in Italian `` Basilica di San Pietro in Vaticano '' , is a large church in the Vatican City , in Rome , Italy . The Papal Basilica of Saint Peter , officially known in Italian as the ' and commonly known as St. Peter 's Basilica , is a Late Renaissance church located within the Vatican City . St. Peter 's Basilica has the largest interior of any Christian church in the world .