The strength of Hatra was great, as had been proved by Trajan and Severus; its thick walls and valiant inhabitants would probably have defied every attempt of the Persian prince to make himself master of it by force. He, therefore, resorted to stratagem. Manizen had a daughter who cherished ambitious views. On obtaining a promise from Sapor that if she gave Hatra into his power he would make her his queen, this unnatural child turned against her father, betrayed him into Sapor's hands, and thus brought the war to an end. Sapor recovered his lost territory; but he did not fulfil his bargain. Instead of marrying the traitoress, he handed her over to an executioner, to receive the death that she had deserved, though scarcely at his hands.
Encouraged by his success in these two lesser contests, Sapor resolved (apparently in a.d. 241) to resume the bold projects of his father, and engage in a great war with Rome. The confusion and troubles which afflicted the Roman Empire at this time were such as might well give him hopes of obtaining a decided advantage. Alexander, his father's adversary, had been murdered in a.d. 235 by Maximin, who from the condition of a Thracian peasant had risen into the higher ranks of the army. The upstart had ruled like the savage that he was, and after three years of misery the whole Roman world had risen against him. Two emperors had been proclaimed in Africa. On their fall two others had been elected by the senate; a third, a mere boy, had been added at the demand of the Roman populace. All the pretenders except the last had met with violent deaths; and after the shocks of a year, unparalleled since a.d. 69, the administration of the greatest kingdom in the world was in the hands of a youth of fifteen. Sapor, no doubt, thought he saw in this condition of things an opportunity that he ought not to miss, and rapidly matured his plans lest the favorable moment should pass away.
Crossing the middle Tigris into Mesopotamia, the bands of Sapor first attacked the important city of Nisibis. Nisibis, at the time a Roman colony, was strongly situated on the outskirts of the mountain range which traverses Northern Mesopotamia between the thirty-seventh and thirty-eighth parallels. The place was well fortified and well defended; it offered a prolonged resistance; but the walls were breached and it was forced to yield itself. The advance was then made along the southern flank of the mountains by Carrhæ (Harran) and Edessa to the Euphrates, which was probably reached in the neighborhood of Birehjik. The hordes then poured into Syria, and, spreading themselves over that fertile region, surprised and took the metropolis of the Roman East, the rich and luxurious city of Antioch. But meantime the Romans had shown a spirit which had not been expected from them.
Gordian, young as he was, had quitted Rome and marched through Mœsia and Thrace into Asia, accompanied by a formidable army and by at least one good general. Timesitheus, whose daughter Gordian had recently married, though his life had hitherto been that of a civilian, exhibited on his elevation to the dignity of prætorian prefect considerable military ability. The army, nominally commanded by Gordian, really acted under his orders. With it Timesitheus attacked and beat the bands of Sapor in a number of engagements, recovered Antioch, crossed the Euphrates, retook Carrhæ, defeated the Persian monarch in a pitched battle near Resaina (Ras-el-Ain), recovered Nisibis, and once more planted the Roman standards on the banks of the Tigris. Sapor hastily evacuated most of his conquests, and retired first across the Euphrates, and then across the more eastern river, while the Romans advanced as he retreated, placed garrisons in the various Mesopotamian towns, and even threatened the great city of Ctesiphon.
Gordian was confident that his general would gain further triumphs, and wrote to the senate to that effect; but either disease or the arts of a rival cut short the career of the victor, and from the time of his death the Romans ceased to be successful. The legions had, it would seem, invaded Southern Mesopotamia when the prætorian prefect who had succeeded Timesitheus brought them intentionally into difficulties by his mismanagement of the commissariat, and at last retreat was determined on.
The young Emperor had almost reached his own frontier, when the discontent of the army, fomented by the prefect, Philip, came to a head. Gordian was murdered at a place called Zaitha, about twenty miles south of Circesium, and was buried where he fell, the soldiers raising a tumulus in his honor. His successor, Philip, was glad to make peace on any tolerable terms with the Persians; he felt himself insecure upon his throne, and was anxious to obtain the senate's sanction of his usurpation. He therefore quitted the East in a.d. 244, having concluded a treaty with Sapor by which Armenia seems to have been left to the Persians, while Mesopotamia returned to its old condition of a Roman province.
The peace made between Philip and Sapor was followed by an interval of fourteen years, during which scarcely anything is known of the condition of Persia. We may suspect that troubles in the northeast of his empire occupied Sapor during this period, for at the end of it we find Bactria, which was certainly subject to Persia during the earlier years of the monarchy, occupying an independent position, and even assuming an attitude of hostility toward the Persian monarch. Bactria had, from a remote antiquity, claims to preëminence among the Aryan nations. She was more than once inclined to revolt from the Achæmenidæ, and during the later Parthian period she had enjoyed a sort of semi-independence. It would seem that she now succeeded in detaching herself altogether from her southern neighbor and becoming a distinct and separate power. To strengthen her position she entered into relations with Rome, which gladly welcomed any adhesions to her cause in this remote region.
Sapor's second war with Rome was, like his first, provoked by himself. After concluding his peace with Philip he had seen the Roman world governed successively by six weak emperors, of whom four had died violent deaths, while at the same time there had been a continued series of attacks upon the northern frontiers of the empire by Alamanni, Goths, and Franks, who had ravaged at will a number of the finest provinces, and threatened the absolute destruction of the great monarchy of the West. It was natural that the chief kingdom of Western Asia should note these events, and should seek to promote its own interests by taking advantage of the circumstances of the time. Sapor, in a.d. 258, determined on a fresh invasion of the Roman provinces, and once more entering Mesopotamia carried all before him, became master of Nisibis, Carrhæ, and Edessa, and, crossing the Euphrates, surprised Antioch, which was wrapped in the enjoyment of theatrical and other representations, and only knew its fate on the exclamation of a couple of actors that "the Persians were in possession of the town!" The aged Emperor, Valerian, hastened to the protection of his more eastern territories, and at first gained some successes, retaking Antioch, and making that city his head-quarters during his stay in the East.
But after this the tide turned. Valerian intrusted the whole conduct of the war to Macrianus, his prætorian prefect, whose talents he admired, and of whose fidelity he did not entertain a suspicion. Macrianus, however, aspired to the empire, and intentionally brought Valerian into difficulties in the hope of disgracing or removing him. His tactics were successful. The Roman army in Mesopotamia was betrayed into a situation whence escape was impossible and where its capitulation was only a question of time. A bold attempt made to force a way through the enemy's lines failed utterly, after which famine and pestilence began to do their work. In vain did the aged Emperor send envoys to propose a peace and offer to purchase escape by the payment of an immense sum in gold. Sapor, confident of victory, refused the overture, and, waiting patiently till his adversary was at the last gasp, invited him to a conference, and then treacherously seized his person. The army surrendered or dispersed. Macrianus, the prætorian prefect, shortly assumed the title of emperor and marched against Gallienus, the son and colleague of Valerian, who had been left to direct affairs in the West. But another rival started up in the East. Sapor conceived the idea of complicating the Roman affairs by himself putting forward a pretender; and an obscure citizen of Antioch, a certain Miriades, or Cyriades, a refugee in his camp, was invested with the purple and assumed the title of Cæsar.
The blow struck at Edessa laid the whole of Roman Asia open to attack, and the Persian monarch was not slow to seize the occasion. His troops crossed the Euphrates in force, and, marching on Antioch, once more captured that unfortunate town, from which the more prudent citizens had withdrawn, but where the bulk of the people, not displeased at the turn of affairs, remained and welcomed the conqueror. Miriades was installed in power, while Sapor himself, at the head of his irresistible squadrons, pressed forward, bursting "like a mountain torrent" into Cilicia, and thence into Cappadocia. Tarsus, the birthplace of St. Paul, at once a famous seat of learning and a great emporium of commerce, fell; Cilicia Campestris was overrun, and the passes of Taurus, deserted or weakly defended by the Romans, came into Sapor's hand.