Saint Peter’s Basilica, or San Pietro in Vaticano as it’s also known, was built between 1506 and 1626 on the site of the Old Saint Peter’s Basilica. The old church was established by the Emperor Constantine the Great in 324 A.D. The site of the old basilica was chosen because it was believed to be the burial place of St. Peter, who is traditionally considered to be the first Bishop of Rome and therefore the first pope and leader of Christendom.