The first siege of Nisibis by Sapor lasted, we are told, sixty-three days. Few particulars of it have come down to us. Sapor had attacked the city, apparently, in the absence of Constantius, who had been called off to Pannonia to hold a conference with his brothers. It was defended, not only by its garrison and inhabitants, but by the prayers and exhortations of its bishop, St. James, who, if he did not work miracles for the deliverance of his countrymen, at any rate sustained and animated their resistance. The result was that the bands of Sapor were repelled with loss, and he was forced, after wasting two months before the walls, to raise the siege and own himself baffled.
After this, for some years the Persian war with Rome languished. It is difficult to extract from the brief statements of epitomizers, and the loose invectives or panegyrics of orators, the real circumstances of the struggle; but apparently the general condition of things was this. The Persians were constantly victorious in the open field; Constantius was again and again defeated; but no permanent gain was effected by these successes. A weakness inherited by the Persians from the Parthians--an inability to conduct sieges to a prosperous issue--showed itself; and their failures against the fortified posts which Rome had taken care to establish in the disputed regions were continual. Up to the close of A.D. 340 Sapor had made no important gain, had struck no decisive blow, but stood nearly in the same position which he had occupied at the commencement of the conflict.
But the year A.D. 341 saw a change. Sapor, after obtaining possession of the person of Tiranus, had sought to make himself master of Armenia, and had even attempted to set up one of his own relatives as king. But the indomitable spirit of the inhabitants, and their firm attachment to their Arsacid princes, caused his attempts to fail of any good result, and tended on the whole to throw Armenia into the arms of Rome. Sapor, after a while, became convinced of the folly of his proceedings, and resolved on the adoption of a wholly new policy. He would relinquish the idea of conquering, and would endeavor instead to conciliate the Armenians, in the hope of obtaining from their gratitude what he had been unable to extort from their fears. Tiranus was still living; and Sapor, we are told, offered to replace him upon the Armenian throne; but, as he had been blinded by his captors, and as Oriental notions did not allow a person thus mutilated to exercise royal power, Tiranus declined the offer made him, and suggested the substitution of his son, Arsaces, who was, like himself, a prisoner in Persia. Sapor readily consented; and the young prince, released from captivity, returned to his country, and was installed as king by the Persians, with the good-will of the natives, who were satisfied so long as they could feel that they had at their head a monarch of the ancient stock. The arrangement, of course, placed Armenia on the Persian side, and gave Sapor for many years a powerful ally in his struggle with Rome.