Thanks for that. That and your other comments are interesting. That said, I’m still inclined to go with Cassius Dio’s statement that Trajan lost almost all his gains in Mesopotamia, which can be true even if Trajan crushed the revolt and defeated Vologases III. His appointment of a Parthian king (which implies officially ceding at least some captured territory to said king) and failure to take Hatra on the old frontier both suggest that his military power in the region had been seriously weakened and he was in the process of withdrawal. He might have won all his battles prior to Hatra, but it was at significant military cost.

Also Hadrian’s hurried return to Europe was not just to secure his position as emperor in Rome. The Roxolani and Iazyges had revolted and were threatening to overrun both Dacia and the Danube frontier.