Ammianus served as an officer in the army of the emperors Constantius II and Julian, he served in Gaul (Julian) and in the east (twice for Constantius, once under Julian). He professes to have been "a former soldier and a Greek" ("miles quondam et graecus"), and his enrollment among the elite "protectores domestici" (household guards) shows that he was of middle class or higher birth. Consensus is that Ammianus probably came from a curial family, but it is also possible that he was the son of a "comes Orientis" of the same family name. He entered the army at an early age, when Constantius II was emperor of the East, and was sent to serve under Ursicinus, governor of Nisibis in Mesopotamia, and "magister militum". Ammianus campaigned in the East twice under Ursicinus.