The present paper deals with the military organization of Near Eastern provinces of the Roman Empire during the reign of Diocletian (AD 284–305). On the basis of the epigraphical evidence published from 1985 to 2015, the author studies which military units defended the Near Eastern frontier of the Empire against the Persian invasions and where these units were deployed. The author pays a special attention to the new military detachments which Diocletian established during his reign.