Rome's first open interference was in Ibera. Iberia had perhaps not been expressly named in the treaty, and support might consequently be given to the expelled Sauromaces without any clear infraction of its conditions. The duke Terentius was ordered, therefore, towards the close of A.D. 370, to enter Iberia with twelve legions and replace upon his throne the old Roman feudatory. Accordingly he invaded the country from Lazica, which bordered it upon the north, and found no difficulty in conquering it as far as the river Cyrus. On the Cyrus, however, he was met by Aspacures, the king of Sapor's choice, who made proposals for an accommodation. Representing himself as really well-inclined to Rome, and only prevented from declaring himself by the fact that Sapor held his son as a hostage, he asked Terentius' consent to a division of Iberia between himself and his rival, the tract north of the Cyrus being assigned to the Roman claimant, and that south of the river remaining under his own government. Terentius, to escape further trouble, consented to the arrangement; and the double kingdom was established. The northern and western portions of Iberia were made over to Sauromaces; the southern and eastern continued to be ruled by Aspacures.
When the Persian king received intelligence of these transactions he was greatly excited. To him it appeared clear that by the spirit, if not by the letter, of the treaty of Dura, Rome had relinquished Iberia equally with Armenia; and he complained bitterly of the division which had been made of the Iberian territory, not only without his consent, but without his knowledge. He was no doubt aware that Rome had not really confined her interference to the region with which she had some excuse for intermeddling, but had already secretly intervened in Armenia, and was intending further intervention. The count Arinthseus had been sent with an army to the Armenian frontier about the same time that Terentius had invaded Iberia, and had received positive instructions to help the Armenians if Sapor molested them. It was in vain that the Persian monarch appealed to the terms of the treaty of Dura--Rome dismissed his ambassadors with contempt, and made no change in her line of procedure. Upon this Sapor saw that war was unavoidable; and accordingly he wasted no more time in embassies, but employed himself during the winter, which had now begun, in collecting as large a force as he could, in part from his allies, in part from his own subjects, resolving to take the field in the spring, and to do his best to punish Rome for her faithlessness.