Called by the emperor Constantine in 325, the first ecumenical (from Greek oikumene, "worldwide") conference of bishops of the Christian church dealt with the problems raised by the Arian opinion of the nature of Jesus Christ - God, man, or some mixture.
The bishops were offered the facilities of the imperial post system - free travel and lodging to and from their episcopal sees to the meeting - to encourage as full an attendance as possible. Constantine formally opened the session.
The Nicene Creed was adopted at this council, and the churches agreed to all celebrate Easter on the same day. The issue of how to establish the date of Easter was not settled until long afterwards however.
- Also see http://www.fordham.edu/halsall/basis/nicea1.txt for a more extensive discussion of the council.
Text to integrate from Schaff-Herzog Encyc of Religion:
I. The First Council, 325 A.D.
1. Character, Membership, and Problems
The first Council of Nice is conspicuous as the starting point for the great doctrinal controversies of the Church in the fourth and fifth centuries. Here a union between the ecclesiastical potency of the councils and the State was effected, vesting the deliberations of this body with imperial power. Earlier synods had been contented with protection against heretical doctrines; but the Council of Nice is characterized by the further step from a defensive position to positive decisions and minutely elaborated articles of faith. In the Arian controversy lay a great obstacle to the realization of Constantine's idea of a universal empire which was to be attained by aid of uniformity of divine worship. Accordingly for the summer of 325 the bishops of all provinces were summoned to the first ecumenical council at Nice in Bithynia, a place easily accessible to the majority of the bishops, especially those of Asia, Syria, Palestine, Egypt, Greece, and Thrace. The number of members can not be accurately stated; Athanasius counted 318, Eusebius only 250. As a matter of course, the oriental bishops formed the preponderating number; the first rank being held by the three archbishops Alexander of Alexandria, Eustathius of Antioch, and Macarius of Jerusalem, and by Eusebius of Nicomedia and Eusebius of Caesarrea. A special prominence attached to this council also because the persecutions had just ended, and it was to be assumed that nearly all of the assembled fathers had stood forth as witnesses of the faith. The occident sent not more than five representatives in equal distribution from the provinces, Marcus of Calabria from Italy, Cecilian of Carthage from Africa, Hosius of Cordova from Spain, Nicasius of Dijon from Gaul, and Domnus of Stridon from the province of the Danube. These ecclesiastical dignitaries of course did not travel alone, but each one with his suite, so that Eusebius speaks of an almost innumerable host of accompanying priests, deacons, and acolytes. Among the assistants it was Athanasius, a young deacon and companion of Bishop Alexander of Alexandria, who distinguished himself as the "most vigorous fighter against the Arians," and similarly Alexander of Constantinople, a presbyter, as representative of his aged bishop. The points to be discussed at the synod were: (1) The Arian question, (2) the celebration of Easter, (3) the Meletian schism, (4) the baptism of heretics, and (5) the status of the lapsed in the persecution under Licinius.
2. The Procedure
The council was formally opened May 20, in the central structure of the imperial palace, busying itself chiefly with preparatory discussions on the Arian question, in which Arius, with some adherents, especially Eusebius of Nicomedia, Theognis of Nice, and Maris of Chalcedon, seems to have been the leading spirit; regular sessions, however, began only on the arrival of the emperor. After prescribing the course of the negotiations he entrusted the mode of procedure to a committee appointed by himself, consisting in all probability of the most prominent participants of that body. It is undoubtedly chiefly owing to this step on the part of Constantine that the council, after being in session for an entire month, promulgated on June 19 the Nicene Creed (see CONSTANTINOPOLITAN CREED). At first the Arians and the orthodox showed an uncompromising front toward each other. The Arians entrusted the representation of their interests to Eusebius of Caesarea (q.v.), whose scholarship and flowery speech made a great impression upon the emperor. His reading of the confession of the Arians called forth a storm of resentment among the opponents; two minorities vividly interested in contrary opinions opposed each other, but between them yawned indifference. In their behalf, as well as for his own sake, Eusebius, after he had ceased to represent the Arians, appeared as a mediator; and in asserting that the chief aim to be pursued should be the establishment of the peace of the Church, he at the same time agreed with his exalted protector. He presented a new formula, the baptismal symbol of his own congregation at Caesarea, by means of which the differing opinions might be reconciled. The emperor, who pursued the purely political intentions of a successful pacification, could desire no more welcome proposition and immediately confirmed it by making it his own. In this way he did not overpower the majority, but most probably met its wishes; for if the orthodox had really been able to count on a preponderating majority, even the predilection of the emperor would not have hindered them from setting up their own confession in the manner of that proposed by Bishop Alexander in his first circular letter. But far from daring such an attempt, the majority (without resistance) complied, asserting their rights only in the form of amending clauses. While such modes of procedure are more characteristic of minorities than of majorities, their use by the latter does not necessarily debar victory, as indeed in this case it did not. All propositions of the orthodox during the remainder of the controversy having been accepted, it is furthermore evident, first: that the Arians of conviction were in the minority; second: that the majority (or deciding body) did not possess, and hence did not assert, convictions of a dogmatic nature. These are, considered in a general way, the presuppositions of the world-important decisions of the Council of Nice.
3. The Symbol
Examining the symbol in detail, it appears that it contained indeed decisions on the Son of God which might satisfy all members of the council. Even Arius found no reason to oppose it from his standpoint. But for the partisans of Bishop Alexander the definitions were too vague; they rendered them more concise, and if the Nicene Creed be compared with its model, that of Caesarea, it seems to have originated in some omissions from the second article which was the only one in question. To these omissions corresponded three no less impor- important additions: (1) to designate the Son "that is, of the essence of the Father" was added; (2) another addition reads " begotten, not made "; (3) the most important addition reads "of one substance with the Father." Of the third article only the words "and in the Holy Ghost" were left and then followed immediately the anathemas. Thus the neutral baptismal confession of the congregation of Caesarea, laid before the council by Eusebius, became the uncompromising anti-Arian symbol of Nice, the text of which is preserved in a letter of Eusebius to his congregation, in Athanasius, and elsewhere. The symbol was finally accepted, although the anti-Arians or Homoousians were in the minority. The emperor was intent upon a decisive settlement of the question; at first he probably had no predilection for either of the conceptions of the two contending parties, but perceiving that the original propositions of Eusebius, which supposedly furthered peace, effected the very opposite, he may involuntarily have considered whether he could not reach his aim more quickly by seeking an agreement with the anti-Arians. Undoubtedly there were not wanting attempts at personal mediation, in the first place on the part of Bishop Hosius of Cordova (q.v.), one of the most decided Homoousians, and at the time of the council the confidant of the emperor in all affairs of the Church. He stands at the head of the lists of participants, and Athanasius ascribes to him the actual success of the symbol. But when it is considered that great men like Eustathius of Antioch, Alexander of Alexandria, Athanasius, and Marcellus of Ancyra belonged to the anti-Arian party, it does not seem strange that the Homoousians, in spite of being in the minority, gained the final victory. Eusebius of Caesarea, in spite of his sympathies for Arius, accepted the decisions of the council, subscribing even the condemnatory clauses against Arius. The number of persons of prominence among the opponents was not so considerable; for after the debates, extending over four weeks, there were only two adherents of Arius who remained steadfast, Theonas of Marmarica in Libya, and Secundus of Ptolemais; of the three others upon whom Arius might have counted, Maria of Chalcedon finally subscribed the whole symbol, Eusebius of Nicomedia and Theognis of Nice at least its positive part, without the condemnatory clauses against Arius. The emperor now actually fulfilled his threat, according to which everybody who refused to sign had to face exile. Arius, Theonas, Secundus, Eusebius of Nicomedia, and Theognis were excommunicated. The works of Arius were confiscated in order to be burnt. But it soon appeared that even force could not silence the disputes, and that under the pressure of such procedure the controversy on the equality of Christ with God assumed unthought-of dimensions; for the Council of Nice had done away with the indifference of the masses to theological distinctions.
4. Other Problems
After the settlement, on June 19, of the most important subject of discussion, the question of Easter was brought up. According to Duchesne (Revue des questions historiques, xxviii. 37), who founds his conclusions (1), on the conciliar letter to the Alexandrians preserved in Theodoret, Hist. eccl., I., ix. 12; Socrates, Hist. eccl., I., ix. 12; (2), on the circular letter of Constantine to the bishops after the council, Eusebius, Vita Constantine, III., xviii. 19; Theodoret, Hist. eccl., I., x. 3 sqq.; (3), on Athanasius, De Synodo, v.; Epist. ad Afros, ii.; the oriental churches of Syria, Cilicia, and Mesopotamia adhered to the Jewish reckoning of the fourteenth of Nisan, instead of basing the calculation for Easter on the equinoctial occurrence after the model of Alexandria and Rome. The council assumed the task of regulating these differences in conformity with the usages of the other churches, because the dependence of some congregations on a Jewish peculiarity was offensive. The Council of Nice, however, did not declare the Alexandrine cycle of Easter as alone canonical, but gave the bishop of Alexandria the privilege of announcing annually the date of Easter to the Roman curia. Although the synod undertook the regulation of the dating of Easter, it contented itself with communicating its decision to the different dioceses, instead of establishing a canon; thus inviting opposition even on this point in due season. Then began the proceedings against the Meletian schism, which, on account of the great popularity of the movement, took an extremely mild development and cost its founder only suspension from office, but no degradation. Finally there followed the prescription of twenty canons or rules of discipline: (1) prohibition of self-castration; (2) establishment of a minimum term for catechizing; (3) prohibition of the presence in the house of a cleric of females who might bring him under suspicion; (4) consecration of a bishop in the presence of at least three provincial bishops and confirmation by the metropolitan; (5) provision for two provincial synods to be held annually; (6) exceptional position granted to Alex andria and Rome as episcopal sees; (7) recognition of the honorary rights of the see of Jerusalem; (8) provision for agreement with the Novatians; (9-14) provision for mild procedure against the lapsed during the persecution under Licinius; (15-16) prohibition of the removal of priests; (17) prohibition of usury among the clergy; (18) precedence of bishops and presbyters over deacons in taking the Eucharist; (19) declaration of the invalidity of baptism by heretics; (20) attitude at prayer on Pentecost.
On July 25, 325, the fathers of the council celebrated the emperor's twentieth anniversary and then dispersed. In his valedictory address the emperor again informed his hearers how averse he was to all dogmatic controversy, and in a circular letter he announced the accomplished unity of practise by the whole Church in the matter of the celebration of Easter. But the illusion of victory did not last, the emperor experiencing stroke after stroke of disappointment and misfortune. The continuation of the synod in 327 questioned every result achieved in 325. Arius as well as the friends punished with him and the Meletians regained nearly all rights which they had lost.