His arms shortly afterwards found employment in another quarter.  The Tatars of the Transoxianian regions were once more troublesome; and in order to check or prevent the incursions which they were always ready to make, if they were unmolested, Isdigerd undertook a long war on his northeastern frontier, which he conducted with a resolution and perseverance not very common in the East.  Leaving his vizier, Mihr-Narses, to represent him at the seat of government, he transferred his own residence to Nishapm, in the mountain region between the Persian and Kharesmian deserts, and from that convenient post of observation directed the military operations against his active enemies, making a campaign against them regularly every year from A.D. 443 to 451.  In the year last mentioned he crossed the Oxus, and, attacking the Ephthalites in their own territory, obtained a complete success, driving the monarch from the cultivated portion of the country, and forcing him to take refuge in the desert.  So complete was his victory that he seems to have been satisfied with the result, and, regarding the war as terminated, to have thought the time was come for taking in hand an arduous task, long contemplated, but not hitherto actually attempted.

This was no less a matter than the forcible conversion of Armenia to the faith of Zoroaster.  It has been already noted that the religious differences which—­from the time when the Armenians, anticipating Constantine, adopted as the religion of their state and nation the Christian faith (ab.  A.D. 300)—­separated the Armenians from the Persians, were a cause of weakness to the latter, more especially in their contests with Rome.  Armenia was always, naturally, upon the Roman side, since a religious sympathy united it with the the court of Constantinople, and an exactly opposite feeling tended to detach it from the court of Ctesiphon.  The alienation would have been, comparatively speaking, unimportant, after the division of Armenia between the two powers, had that division been regarded by either party as final, or as precluding the formation of designs upon the territory which each had agreed should be held by the other.  But there never yet had been a time when such designs had ceased to be entertained; and in the war which Isdigerd had waged with Theodosius at the beginning of his reign, Roman intrigues in Persarmenia had forced him to send an army into that country.  The Persians felt, and felt with reason, that so long as Armenia remained Christian and Persia held to the faith of Zoroaster, the relations of the two countries could never be really friendly; Persia would always have a traitor in her own camp; and in any time of difficulty—­especially in any difficulty with Rome—­might look to see this portion of her territory go over to the enemy.  We cannot be surprised if Persian statesmen were anxious to terminate so unsatisfactory a state of things, and cast about for a means whereby Armenia might be won over, and made a real friend instead of a concealed enemy.