9, ad fin.
It seems to have been soon after the close of Sapor's first war with Constantius that events took place in Armenia which once more replaced that country under Roman influence.

Arsaces, the son of Tiranus, had been, as we have seen, established as monarch, by Sapor, in the year A.D.341, under the notion that, in return for the favor shown him, he would administer Armenia in the Persian interest.

But gratitude is an unsafe basis for the friendships of monarchs.

Arsaces, after a time, began to chafe against the obligations under which Sapor had laid him, and to wish, by taking independent action, to show himself a real king, and not a mere feudatory.

He was also, perhaps, tired of aiding Sapor in his Roman war, and may have found that he suffered more than he gained by having Rome for an enemy.