Meantime the angry prince, convinced at last against his will that negotiations with such an enemy were futile, collected an army and began his march towards the East. Taking troops from the various provinces through which he passed, he conducted to Antioch, in the autumn of A.D. 231, a considerable force, which was there augmented by the legions of the East and by troops drawn from Egypt and other quarters. Artaxerxes, on his part, was not idle. According to Soverus himself, the army brought into the field by the Persian monarch consisted of one hundred and twenty thousand mailed horsemen, of eighteen hundred scythed chariots, and of seven hundred trained elephants, bearing on their backs towers filled with archers; and though this pretended host has been truly characterized as one "the like of which is not to be found in Eastern history, and has scarcely been imagined in Eastern romance," yet, allowing much for exaggeration, we may still safely conclude that great exertions had been made on the Persian side, that their forces consisted of the three arms mentioned, and that the numbers of each were large beyond ordinary precedent. The two adversaries were thus not ill-matched; each brought the flower of his troops to the conflict; each commanded the army, on which his dependence was placed, in person; each looked to obtain from the contest not only an increase of military glory, but substantial fruits of victory in the shape of plunder or territory.
It might have been expected that the Persian monarch, after the high tone which he had taken, would have maintained an aggressive attitude, have crossed the Euphrates, and spread the hordes at his disposal over Syria, Cappadocia, and Asia Minor. But it seems to be certain that he did not do so, and that the initiative was taken by the other side. Probably the Persian arms, as inefficient in sieges as the Parthian, were unable to overcome the resistance offered by the Roman forts upon the great river; and Artaxerxes was too good a general to throw his forces into the heart of an enemy's country without having first secured a safe retreat. The Euphrates was therefore crossed by his adversary in the spring of A.D. 232; the Roman province of Mesopotamia was easily recovered; and arrangements were made by which it was hoped to deal the new monarchy a heavy blow, if not actually to crush and conquer it.