<P> By the fifth century, Christendom was divided into a pentarchy of five sees with Rome accorded a primacy . The four Eastern sees of the pentarchy, considered this determined by canonical decision and did not entail hegemony of any one local church or patriarchate over the others . However, Rome began to interpret her primacy in terms of sovereignty, as a God - given right involving universal jurisdiction in the Church . The collegial and conciliar nature of the Church, in effect, was gradually abandoned in favour of supremacy of unlimited papal power over the entire Church . These ideas were finally given systematic expression in the West during the Gregorian Reform movement of the eleventh century . The Eastern churches viewed Rome's understanding of the nature of episcopal power as being in direct opposition to the Church's essentially conciliar structure and thus saw the two ecclesiologies as mutually antithetical . For them, specifically, Simon Peter's primacy could never be the exclusive prerogative of any one bishop . All bishops must, like St. Peter, confess Jesus as the Christ and, as such, all are Peter's successors . The churches of the East gave the Roman See, primacy but not supremacy . The Pope being the first among equals, but not infallible and not with absolute authority . </P> <P> The other major irritant to Eastern Christendom was the Western use of the filioque clause--meaning "and the Son"--in the Nicene Creed . This too developed gradually and entered the Creed over time . The issue was the addition by the West of the Latin clause filioque to the Creed, as in "the Holy Spirit...who proceeds from the Father and the Son," where the original Creed, sanctioned by the councils and still used today, by the Eastern Orthodox simply states "the Holy Spirit, the Lord and Giver of Life, who proceeds from the Father ." The Eastern Church argued that the phrase had been added unilaterally and, therefore, illegitimately, since the East had never been consulted . In the final analysis, only another ecumenical council could introduce such an alteration . Indeed, the councils, which drew up the original Creed, had expressly forbidden any subtraction or addition to the text . In addition to this ecclesiological issue, the Eastern Church also considered the filioque clause unacceptable on dogmatic grounds . Theologically, the Latin interpolation was unacceptable since it implied that the Spirit now had two sources of origin and procession, the Father and the Son, rather than the Father alone . </P> <P> In the 9th century AD, a controversy arose between Eastern (Byzantine, later Orthodox) and Western (Latin, later Roman Catholic) Christianity that was precipitated by the opposition of the Roman Pope John VIII to the appointment by the Byzantine emperor Michael III of Photius I to the position of patriarch of Constantinople . Photios was refused an apology by the pope for previous points of dispute between the East and West . Photius refused to accept the supremacy of the pope in Eastern matters or accept the filioque clause . The Latin delegation at the council of his consecration pressed him to accept the clause in order to secure their support . </P> <P> The controversy also involved Eastern and Western ecclesiastical jurisdictional rights in the Bulgarian church, as well as a doctrinal dispute over the Filioque ("and from the Son") clause . That had been added to the Nicene Creed by the Latin church, which was later the theological breaking point in the ultimate Great East - West Schism in the eleventh century . </P>

Who evolved as head of the roman catholic church during the middle ages