The pontifex maximus (Latin for "supreme pontiff") was the chief high priest of the College of Pontiffs (Collegium Pontificum) in ancient Rome. This was the most important position in the ancient Roman religion, open only to patricians until 254 BC, when a plebeian first occupied this post. Although in fact the most powerful office in the Roman priesthood, the pontifex maximus was officially ranked fifth in the ranking of the highest Roman priests (ordo sacerdotum), behind the rex sacrorum and the flamines maiores (Flamen Dialis, Flamen Martialis, Flamen Quirinalis).
A distinctly religious office under the early Roman Republic, it gradually became politicized until, beginning with Augustus, it was subsumed into the position of emperor in the Roman imperial period. Subsequent emperors were styled pontifex maximus well into Late Antiquity, including Gratian (r. 367–383), but during Gratian's reign the phrase was replaced in imperial titulature with the Latin phrase: pontifex inclytus ("honourable pontiff"), an example followed by Gratian's junior co-emperor Theodosius the Great and which was used by emperors thereafter including the co-augusti Valentinian III (r. 425–455) and Marcian (r. 450–457) and the augustus Anastasius Dicorus (r. 491–518). The first to adopt the inclytus alternative to maximus may have been the rebel augustus Magnus Maximus (r. 383–388).
The word pontifex and its derivative "pontiff" became terms used for Christian bishops, including the Bishop of Rome, and the title of pontifex maximus was applied to the Roman Catholic Church for the pope as its chief bishop and appears on buildings, monuments and coins of popes of Renaissance and modern times. The official list of titles of the pope given in the Annuario Pontificio includes "supreme pontiff" (Latin: summus pontifex) as the fourth title, the first being "bishop of Rome".
In the matter of hierarchical nomenclature, one of the most striking instances is the adoption of the term pontifex for a bishop