Lactantius

“ Diocletian, apt to be low-spirited and timorous in every commotion, and fearing a fate like that of Valerian, would not in person encounter Narseus; but he sent Galerius by the way of Armenia, while he himself halted in the eastern provinces, and anxiously watched the event. It is a custom amongst the barbarians to take everything that belongs to them into the field. Galerius laid an ambush for them, and easily overthrew men embarrassed with the multitude of their followers and with their baggage. ”

“ The cause was this. Narseus, king of the Persians, emulating the example set him by his grandfather Sapores, assembled a great army, and aimed at becoming master of the eastern provinces of the Roman empire. ”