325 – Council of Nicaea prepares a creed, recognizing Christ as eternal and of the same essence as the Father.
http://www.christianhistoryinstitute.org/today/6/19
This first ecumenical council was the first effort to attain consensus in the church through an assembly representing all of Christendom, although previous councils, including the first Church council, the Council of Jerusalem, had met before to settle matters of dispute. It was presided over by Hosius, bishop of Corduba.
Its main accomplishments were settlement of the Christological issue of the nature of the Son of God and his relationship to God the Father, the construction of the first part of the Creed of Nicaea, establishing uniform observance of the date of Easter,and promulgation of early canon law.
http://en.wikipedia.org/wiki/First_Council_of_Nicaea
