While Sapor was thus engaged in the far East, he received letters from the officer whom he had left in charge of his western frontier, informing him that the Romans were anxious to exchange the precarious truce which Mesopotamia had been allowed to enjoy during the last five or six years for a more settled and formal peace. 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. His letter, which was conveyed to the Roman emperor at Sirmium by an ambassador named Narses, was conceived in the following terms:
"Sapor, king of kings, brother of the sun and moon, and companion of the stars, sends salutation to his brother, Constantius Caesar. It glads me to see that thou art at last returned to the right way, and art ready to do what is just and fair, having learned by experience that inordinate greed is oft-times punished by defeat and disaster. As then the voice of truth ought to speak with all openness, and the more illustrious of mankind should make their words mirror their thoughts, I will briefly declare to thee what I propose, not forgetting that I have often said the same things before. Your own authors are witness that the entire tract within the river Strymon and the borders of Macedon was once held by my ancestors; if I required you to restore all this, it would not ill become me (excuse the boast), inasmuch as I excel in virtue and in the splendor of my achievements the whole line of our ancient monarchs. But as moderation delights me, and has always been the rule of my conduct--wherefore from my youth up I have had no occasion to repent of any action--I will be content to receive Mesopotamia and Armenia, which was fraudulently extorted from my grandfather. We Persians have never admitted the principle, which you proclaim with such effrontery, that success in war is always glorious, whether it be the fruit of courage or trickery. In conclusion, if you will take the advice of one who speaks for your good, sacrifice a small tract of territory, one always in dispute and causing continual bloodshed, in order that you may rule the remainder securely. Physicians, remember, often cut and burn, and even amputate portions of the body, that the patient may have the healthy use of what is left to him; and there are animals which, understanding why the hunters chase them, deprive themselves of the thing coveted, to live thenceforth without fear. I warn you, that, if my ambassador returns in vain, I will take the field against you, so soon as the winter is past, with all my forces, confiding in my good fortune and in the fairness of the conditions which I have now offered."