These movements were seen with no small disquietude by the Persian king.  The army which he had regarded as almost a certain prey seemed about to escape him.  He knew that his troops could not pass the Tigris by swimming; he had, it is probable, brought with him no boats, and the country about Dura could not supply many; to follow the Romans, if they crossed the stream, he must construct a bridge, and the construction of a bridge was, to such unskilful engineers as the Persians, a work of time.  Before it was finished the legions might be beyond his reach, and so the campaign would end, and he would have gained no advantage from it.  Under these circumstances he determined to open negotiations with the Romans, and to see if he could not extract from their fears some important concessions.  They were still in a position of great peril, since they could not expect to embark and cross the stream without suffering tremendous loss from the enemy before whom they would be flying.  And it was uncertain what perils they might not encounter beyond the river in traversing the two hundred miles that still separated them from Roman territory.  The Saracenic allies of Persia were in force on the further side of the stream; and a portion of Sapor’s army might be conveyed across in time to hang on the rear of the legions and add largely to their difficulties.  At any rate, it was worth while to make overtures and see what answer would be returned.  If the idea of negotiating were entertained at all, something would be gained; for each additional day of suffering and privation diminished the Roman strength, and brought nearer the moment of absolute and complete exhaustion.  Moreover, a bridge might be at once commenced at some little distance, and might be pushed forward, so that, if the negotiations failed, there should be no great delay in following the Romans across the river.

Such were probably the considerations which led Sapor to send as envoys to the Roman camp at Dura the Surena and another great noble, who announced that they came to offer terms of peace.  The great king, they said, having respect to the mutability of human affairs, was desirous of dealing mercifully with the Romans, and would allow the escape of the remnant which was left of their army, if the Caesar and his advisers accepted the conditions that he required.  These conditions would be explained to any envoys whom Jovian might empower to discuss them with the Persian plenipotentiaries.  The Roman emperor and his council gladly caught at the offer; and two officers of high rank, the general Arinthseus and the prefect Sallust, were at once appointed to confer with Sapor’s envoys, and ascertain the terms on which peace would be granted.  They proved to be such as Roman pride felt to be almost intolerable; and great efforts were made to induce Sapor to be content with less.  The negotiations lasted for four days; but the Persian monarch was inexorable; each day diminished his adversary’s strength and bettered his own position; there was no reason why he should make any concession at all; and he seems, in fact, to have yielded nothing of his original demands, except points of such exceedingly slight moment that to insist on them would have been folly.