He therefore committed the task of reinstating Tiridates and punishing Narses to his favorite and son-in-law, Galerius, while he himself took up a position within the limits of the empire, which at once enabled him to overawe his domestic adversaries and to support and countenance his lieutenant.
The first attempts of Galerius were unfortunate.

Summoned suddenly from the Danube to the Euphrates, and placed at the head of an army composed chiefly of the levies of Asia, ill-disciplined, and unacquainted with their commander, he had to meet an adversary of whom he knew little or nothing, in a region the character of which was adverse to his own troops and favorable to those of the enemy.

Narses had invaded the Roman province of Mesopotamia, had penetrated to the Khabour, and was threatening to cross the Euphrates into Syria.

Galerius had no choice but to encounter him on the ground which he had chosen.

Now, though Western Mesopotamia is ill-described as a smooth and barren surface of sandy desert, without a hillock, without a tree, and without a spring of fresh water, it is undoubtedly an open country, possessing numerous plains, where, in a battle, the advantage of numbers is likely to be felt, and where there is abundant room for the evolutions of cavalry.
The Persians, like their predecessors the Parthians, were especially strong in horse; and the host which Narses had brought into the field greatly outnumbered the troops which Diocletian had placed at the disposal of Galerius.