The Ecclesiastical History of Sozomen 88Campaign of Constantius in Sirmium, and Details concerning Vetranio and Magnentius. Gallus receives the Title of Cæsar, and is sent to the East.

On the expulsion of Athanasius, which took place about this period, George persecuted all those throughout Egypt who refused to conform to his sentiments. The emperor marched into Illyria, and entered Sirmium, whither Vetranio had repaired by appointment. The soldiers who had proclaimed him emperor suddenly changed their mind, and saluted Constantius as sole sovereign, and as Augustus, for both the emperor and his supporters, strove for this very action. Vetranio perceived that he was betrayed, and threw himself as a suppliant at the feet of Constantius. Constantius pitied him indeed, but stripped him of the imperial ornaments and purple, obliged him to return to private life, liberally provided for his wants out of the public treasury, and told him that it was more seemly to an old man to abstain from the cares of empire and to live in quietude. After terminating these arrangements in favor of Vetranio, Constantius sent a large army into Italy against Magnentius. He then conferred the title of Caesar on his cousin Gallus, and sent him into Syria to defend the provinces of the East.