The coming to power of the Sassanian Dynasty in Iran in AD 224 opens a new chapter in the struggle for hegemony in the Near East. Till then, Rome’s fortunes had fared reasonably well in its perennial conflict with the Parthians. The ignominy of Crassus’ defeat at Carrhae was little more than a schoolboy jingle: ‘Carrhas Crassi clade nobiles’ (Carrhae whose name was renowned by reason of her defeat of Crassus) and it certainly did not compel commanders like Corbulo to regard the Euphrates as a sacred barrier to ambition and fame. Though Trajan’s sweeping conquests at the beginning of the second century in Mesopotamia were mostly abandoned by his immediate successors, Roman power gradually reasserted itself east of the Euphrates as the century progressed. The Parthian Wars of Lucius Verus in 165 saw the formal incorporation of the Euphrates corridor into the Roman sphere of influence with Roman troops garrisoned as far south as Salihiye (Dura Europos), Ana (Anatha), and Kifrin. The oasis city of Palmyra, a Roman colony since the time of Hadrian, contributed to the stability on the southern flanks by acting as policeman of the Syrian Desert. More importantly, Septimius Severus created the new province of Osrhoene c. 197, confining the power of the Abgars, renowned for their political vacillations, to the city of Edessa and its immediate environs. The new network of roads allowed Nisibis and Singara to be more firmly integrated into Rome’s eastern defences, giving her valuable access to the Tigris and a choice of invasion routes. Thus, when Opelius Macrinus withdrew the army of the murdered Caracalla, whose Praetorian Prefect he was, from Mesopotamia after an indecisive battle with the Parthian king Artabanus V near Nisibis in 217, few would have predicted any major change in the balance of power. Both sides seemed set for a period of minor wars and the consolidation of their existing frontiers.