342/343–344

The Council of Serdica

At the proposal of Emperor Constans, bishops of East and West gathered at Serdica under the presidency of Hosius of Cordoba. Athanasius, exiled from the East, was received in the West with open arms. The western councils at Rome (341) and Serdica unreservedly confirmed his teaching.

The eastern bishops saw that the excommunicated Athanasius and Marcellus of Ancyra had been given a voice. So they withdrew to Philippopolis. There they deposed their opponents' supporters and adopted a creed directed against Marcellus.

The westerners, remaining at Serdica itself, vindicated Marcellus and Athanasius. They adopted a "rule of faith" speaking of a single hypostasis, and a canon allowing deposed bishops to appeal to Rome. The council split the church into two hostile camps and exposed the rivalry between Rome and Constantinople.