The First Ecumenical Council (Nicaea, 325)

In the early 4th century Arius, a presbyter of Alexandria, taught that the Son of God was created by the Father and that “there was when He was not”. The dispute spread across the Eastern Churches. After the Edict of Milan (313) the Emperor Constantine sought church unity and summoned the bishops to Nicaea (Bithynia, Asia Minor) in the summer of 325.

The Council rejected the teaching of Arius and confessed the Son “consubstantial” (Greek homoousios) with the Father. It composed a Creed, later completed by the Second Ecumenical Council. It decided that all Churches should celebrate Pascha on the same day; the actual paschal tables were worked out later in Alexandria. Twenty canons on church order and penitential discipline were adopted.

Church tradition counts 318 fathers at the Council; historians estimate roughly 250–300 participants. The Nicene faith was defended by Alexander of Alexandria and his deacon Athanasius, the future St Athanasius the Great. The presence of St Nicholas of Myra and St Spyridon of Trimythous is known from church tradition.

The Arian controversy did not end: for several decades the Nicene confession was contested until the Second Ecumenical Council confirmed it.