Res Gestae

Such was the series of events in Gaul. While they were going on so successfully and so wisely, Constantius sent for Arsaces, king of Armenia, and after entertaining him with the greatest generosity forewarned and urged him to continue to be faithful and friendly to us.

For he heard that he had often been worked upon by the Persian king with deception, with threats, and with guile, to induce him to give up his alliance with the Romans and involve himself in the Persian’s designs.

And the king, swearing with many an oath that he could sooner give up his life than his resolve, after receiving rewards returned to his kingdom with the retinue that he had brought with him; and after that he never dared to violate any of his promises, being bound to Constantius by many ties of gratitude, among which this was especially strong-that the emperor had given him to wife Olympias, daughter of Ablabius, a former praetorian prefect, and the betrothed of his brother Constans.