The Diocletian system arose in the middle of the third century when the political and military problems Rome was facing posed a significant threat to her stability. The new structure utilized a shallow “defense in depth” strategy to replace the massed force model. As in the Antonine system, there was no surplus of military power for offensive use or deterrent, but unlike its predecessor, the Diocletian system had no “surge” capability.
The concept of defense was one of containment. Because forces had to be put together ad hoc according to circumstances, penetrations were commonplace and the threat of Roman power was everywhere absent. Any diplomacy undertaken with external powers was local and dependent on the availability of forces. The outputs and inputs to the military system had finally come into balance and security was equal to the size of the force put to the task of maintaining it.