Two great Roman officials, Cassianus, duke of Mesopotamia, and Musonianus, Praetorian prefect, understanding that Sapor was entangled in a bloody and difficult war at the eastern extremity of his empire, and knowing that Constantius was fully occupied with the troubles caused by the inroads of the barbarians into the more western of the Roman provinces, had thought that the time was favorable for terminating the provisional state of affairs in the Mesopotamian region by an actual treaty.

They had accordingly opened negotiations with Tamsapor, satrap of Adiabene, and suggested to him that he should sound his master on the subject of making peace with Rome.

Tamsapor appears to have misunderstood the character of these overtures, or to have misrepresented them to Sapor; in his despatch he made Constantius himself the mover in the matter, and spoke of him as humbly supplicating the great king to grant him conditions.

It happened that the message reached Sapor just as he had come to terms with his eastern enemies, and had succeeded in inducing them to become his allies.

He was naturally elated at his success, and regarded the Roman overture as a simple acknowledgment of weakness.
Accordingly he answered in the most haughty style.