<P> The First Council of Nicaea, held in Nicaea in Bithynia (in present - day Turkey), convoked by Roman Emperor Constantine I in 325, was the first ecumenical conference of bishops of the Catholic Church (Catholic as in' universal', not just Roman) and most significantly resulted in the first declaration of a uniform Christian doctrine . </P> <P> The purpose of the council was to resolve disagreements in the Church of Alexandria over the nature of Jesus in relationship to the Father; in particular, whether Jesus was of the same substance as God the Father or merely of similar substance . Alexander of Alexandria and Athanasius took the first position; the popular presbyter Arius, from whom the term Arian controversy comes, took the second . The council decided against the Arians overwhelmingly (of the estimated 250--318 attendees, all but 2 voted against Arius). Another result of the council was an agreement on the date of the Christian Passover (Pascha in Greek; Easter in modern English), the most important feast of the ecclesiastical calendar . The council decided in favour of celebrating the resurrection on the first Sunday after the first full moon following the vernal equinox, independently of the Bible's Hebrew Calendar, and authorized the Bishop of Alexandria (presumably using the Alexandrian calendar) to announce annually the exact date to his fellow bishops . </P> <P> The council was historically significant because it was the first effort to attain consensus in the church through an assembly representing all of Christendom . With the creation of the Nicene Creed, a precedent was established for subsequent general councils to create a statement of belief and canons which were intended to become guidelines for doctrinal orthodoxy and a source of unity for the whole of Christendom--a momentous event in the history of the Church and subsequent history of Europe . </P> <P> The council was opposed by the Arians, and Constantine tried to reconcile Arius with the Church . Even when Arius died in 336, one year before the death of Constantine, the controversy continued, with various separate groups espousing Arian sympathies in one way or another . In 359, a double council of Eastern and Western bishops affirmed a formula stating that the Father and the Son were similar in accord with the scriptures, the crowning victory for Arianism . The opponents of Arianism rallied, but in the First Council of Constantinople in 381 marked the final victory of Nicene orthodoxy within the empire, though Arianism had by then spread to the Germanic tribes, among whom it gradually disappeared after the conversion of the Franks to Catholicism in 496 . </P>

Which of these helped rome claim a special place in christendom by the 400s