Heather begins by distinguishing local from central Romanness. Central Romanness -- a central court, bureaucracy, and system of law that responded to the interests of the landowning class, and a professional army to protect this order -- died in the 470s. With its demise the great centripetal force drawing the peoples of the west to Roman cultural identity disappeared. But local Romanness -- the cultural and ideological attachment to being Roman -- was slow a-dying. For more than a century after the end of the empire in the West, there was a significant section of elite population who were culturally and even legally Roman.
Heather takes a synoptic view of the three stages of the fall of central Romanness -- 1) the invasions of the late 4th and early 5th centuries; (2) progressively more debilitating carving out of domains within the empire by barbarian groups in the first three-quarters of the 5th century; (3) the final seizure of fully independent kingdoms by the barbarians when the empire was no longer able to stand up to them. He argues that the Huns drove the initial invasions, that their presence helped prevent further invasions in the 5th century and helped the Romans to control the previous invaders, and that the Hunnic collapse threw the balance of power decisively in favor of the barbarians.
The end of the Roman state did take away the incentive for local elites to maintain classical literary education, local civic life, and the other aspects of local Romanness. Military service rather than Romanness became the path to getting ahead.
Although Heather's rejects Gibbons' thesis that internal factors alone were the cause of Rome's fall -- pointing to the survival of the Eastern Empire as a decisive refutation -- he does acknowledge that the military, economic, and political limits of The Roman Empire interacted in decisive ways with the external invaders who brought down the Empire. Militarily, the Romans ability to contain the barbarians was limited because the Sasanian front required a quarter of the Empire's armed force. This military force could not simply be further expanded because there was no way to generate more revenue -- agricultural production was already at its maximum. Politically, the empire was brittle in the face of barbarian invasion because local landowning elites -- the bulwark of imperial support -- had to swing their support behind any new power in their region to retain their property. Moreover, the Empire was beset by demands from a vast breadth of local elites, and to satisfy these demands it had to resort divided imperial rule. It was never possible to really settle the division of power or the management of succession, however, so this dual system was subject to prolonged bouts of instability during which the barbarians were able to press their advantage.
The external factor in the fall of Rome -- the powerful groups of invading barbarians -- depended on integration of Germanic tribes into larger coalitions. This process was driven by fear and opportunity: fear of the power of the Roman state against isolated opponents and the opportunity to seize enormous wealth if sufficient force could be mustered. These factors had actually been at play (along with the increasing wealth of Germania itself) in consolidating Germanic political units for centuries before the invasions.
A couple of notes on the text: (1) There is a fair bit of repetition of ideas and even phrases in the last three chapters -- it could have done with more editing polish. (2) Throughout the work, the maps fail to provide enough detail. There are many significant features referred to in the text (example: the passes over the Haemus mountains) which cannot be identified in the maps.
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