But then the Arians, seeing that stratagem did not succeed, determined to proceed by force. For it was easy for those to attempt and carry out anything who were supported by the favor of the monarch, whom they had thoroughly won over to themselves by wicked flatteries. Moreover, they were by the consent of all unconquerable; for almost all the bishops of the two Pannonias, and many of the Eastern bishops, and those throughout all Asia, had joined in their unfaithfulness. But the chief men in that evil company were Ursatius of Singidunum, Valens of Mursa, Theodorus of Heraclia, Stephanus of Antioch, Acatius of Cæsarea, Menofantus of Ephesus, Georgius of Laodicia, and Narcissus of Neronopolis.
These had got possession of the palace to such an extent that the emperor did nothing without their concurrence. He was indeed at the beck of all of them, but was especially under the influence of Valens. For at that time, when a battle was fought at Mursa against Magnentius, Constantius had not the courage to go down to witness for himself the conflict, but took up his abode in a church of the martyrs which stood outside the town, Valens who was then the bishop of the place being with him to keep up his courage.
But Valens had cunningly arranged, through means of his agents, that he should be the first to be made acquainted with the result of the battle. He did this either to gain the favor of the king, if he should be the first to convey to him good news, or with a view to saving his own life, since he would obtain time for flight, should the issue prove unfortunate. Accordingly, the few persons who were with the king being in a state of alarm, and the emperor himself being a prey to anxiety, Valens was the first to announce to them the flight of the enemy.
When Constantius requested that the person who had brought the news should be introduced to his presence, Valens, to increase the reverence felt for himself, said that an angel was the messenger who had come to him. The emperor, who was easy of belief, was accustomed afterwards openly to declare that he had won the victory through the merits of Valens, and not by the valor of his army.
Source: Sacred History (New Advent)