(EN) F. A. Sullivan, Pope, in The New Catholic Encyclopedia, vol. 11, New York, Gale, 2002, pp. 495-496.
«The office of the pope is described in the Annuario pontificio (official directory of the HOLY SEE) by the following titles: "Bishop of Rome, Vicar of Jesus Christ, Successor of the Chief of the Apostles, Supreme Pontiff of the Universal Church, Patriarch of the West, Primate of Italy, Archbishop and Metropolitan of the Roman Province, Sovereign of the State of Vatican City." Of these titles, the basis of all the rest is the third, Successor of the Chief of the Apostles. VATICAN COUNCIL I defined that Christ constituted St. PETER chief of all the APOSTLES and visible head of the whole Church militant, granting him a PRIMACY not merely of honor but of true jurisdiction; that Christ established that Peter should have perpetual successors in this primacy; and that the Roman bishops are these successors (Enchiridion symbolorum 3055, 3058)»
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