This was in many ways the logical conclusion of Roman administrative policy along the frontier. Romanization was never really a policy of raising native peoples to the level of Roman culture, but an administrative device with which to control the inhabitants of the provinces. Nor was Roman citizenship really a recognition of merit and service so much as a means of detaching native aristocracies from their peoples and creating a source of recruits to fill the ranks of the legions. Since the time of Augustus, the goal of Roman policy had been to establish a fixed frontier on which as much of the cost as possible would be borne by the native inhabitants. By the third century, this goal had, for all intents and purposes, been reached. The burden of defense had been placed entirely on the shoulders of the inhabitants of the frontier districts.
They met this challenge far better than one might have expected. Although the frontier defenses were occasionally breached, and the imperial government had to invest vast sums in maintaining a mounted field force composed of German mercenaries, the empire's defenses in the West held for some two centuries longer. Even then, much of the responsibility for the final defeat was due to the insistence of the imperial high command on stripping the western frontiers of troops in order to defend an Italy that had many years before ceased to carry its own weight in the empire.