Almost from its very inception, the Roman imperial administration realized that its economic and human resources were insufficient to support continued Roman expansion and barely adequate to defend the frontiers of those lands that had already been acquired. Moreover, the Italian heartland of the empire had been exhausted by civil wars that had accompanied the fall of the republic and never recovered its earlier vigor and vitality. The traditional Roman sources of manpower, money, and material continued to dwindle during the early imperial period. One last effort at expansion was conducted under the emperor Augustus and had to be abandoned in the face of determined resistance. It was clear to Augustus and most of his immediate successors that the empire no longer possessed the power to conquer and subdue more hostile territory. The immediate task became that of finding and manning defensible boundaries. By the middle of the first century A.D., Roman legions had taken up positions in Britain and along the Rhine and Danube rivers, and were industriously constructing a fortified and fixed defensive frontier. Except for some relatively minor and temporary adjustments, this line was held until the final crumbling of the Roman Empire in the West during the course of the fifth century.
The conquest and occupation of these border provinces and frontier districts caused dramatic changes, altering the physical aspect of the land and transforming the economic, social, and political structure of