Eunomius, who had studied theology at Alexandria under Aëtius, and afterwards come under the influence of Eudoxius of Antioch, who ordained him deacon, had in 360 been appointed bishop of Cyzicus, in Mysia, on the recommendation of Eudoxius.

Propounding an extreme form of Arianism that refutes the divinity of Christ and constructing his argument on a Platonist philosophical structure, Eunomius teaches that Christ was not equal to God the Father but only resembled him.

Here his free utterance of extreme Arian views have led to popular complaints, and Eudoxius is compelled, by command of Constantius, to depose him from the bishopric within a year of his elevation to it.