The Papal Basilica of St. Paul outside the Walls is one of Rome's 4 ancient, Papal, major basilicas. The Basilica is within Italian territory and not the territory of the Vatican City State. However, the Holy See fully owns the Basilica, andItaly is legally obligated to recognize its full ownership thereof and to concede to it "the immunity granted by International Law to the headquarters of the diplomatic agents of foreign States". The Basilica was founded by the Roman Emperor Constantine I over the burial place of St. Paul, where it was said that, after the Apostle's execution, his followers erected a memorial, called a cella memoriae.