Emperors, Frontiers and Foreign Relations, 31 b.c. to a.d. 378

Severus…. was in the habit of saying that he had gained a large additional territory and made it a bulwark for Syria. But the facts themselves show that it is a source of continual wars for us, and of great expenses. For it provides very little revenue and involves very great expenditure; and having extended our frontiers to the neighbours of the Medes and Parthians, we are constantly so to speak at war in their defence.’ So writes Cassius Dio about the extension of the Eastern frontier in the 190s and the creation of the provinces of Mesopotamia and Osrhoene. The significance of the passage however, extends beyond the question of the Eastern frontier itself at that moment. Written by an ex-consul, and former assessor of Severus, it reveals two types of justification for conquest uttered by the Emperor himself - one straightforwardly imperialistic, the other strategic; and a critique of this from two points of view, the balance of income and expenditure, and the wider strategic commitments incurred. Whether Dio had formulated such views already in Severus’ reign we cannot know; this section of his History will have been written at the earliest towards 220, and probably later. If he had, we have no reason to think that he expressed them to Severus. If he did, it can only have been after the event, for his own narrative at this point makes clear that the new province of Mesopotamia was entrusted to an eques, and an ‘honour’ (the status of colonia) given to Nisibis, either after the campaign of 195, or (less probably) after that of 198, in neither of which Dio himself took part. None the less, the fact that the passage retails both the authentic views of an Emperor and a critique of them by a consularis may encourage us to ask some general questions: how, by whom and within what conceptual frameworks were the foreign and frontier ‘policies’ of the Empire formulated?