There is much about these second- and third-century migration flows that will always remain beyond our grasp. The available evidence does not allow us to explore precise trigger factors in detail, nor to ask which individuals were ready to participate, and why, when many of their neighbours stayed at home. But the evidence is good enough to establish that migration was a major factor in the reconstruction of the frontiers of Roman Europe. ‘Development’ – processes of sociopolitical and economic transformation resulting in the new confederations of the late imperial period – was also central to the action. But an anti-migrationist reading of the evidence has to discount too much archaeological and historical evidence, and spectacularly fails to explain the cultural shift in the nature of Rome’s main partners across the Lower Danube and Black Sea frontiers. Further west, the migration element was less dramatic, but perfectly distinct nonetheless in the Alamannic occupation of the Agri Decumates and the arrival of substantial numbers of Burgundians on the River Main.
The evidence also establishes the interconnections here between migration and development. The two are not alternative lines of explanation, as they have sometimes been portrayed, but essentially intertwined in the unfolding of events, and on many levels. First, the process of development in Germanic society was itself a fundamental cause of the migration flows, both negatively – by making its internal workings so violently competitive that some may have sought safer homes elsewhere – and positively, in the sense that the new wealth of the immediate frontier zone encouraged groups from the outer periphery to move in and displace the sitting tenants. Contact with the Roman Empire was generating considerable but geographically disparate development in Germania, and, as in the modern world, marked differences in wealth acted as a spur to migration. Second, the mechanism by which this new wealth had largely been generated – being Rome’s preferred partner on a particular section of the frontier – also explains part of the seeming oddity of the resulting migration flow. These centuries saw nothing so simple as the old invasion hypothesis at work. Numerous separate expeditions, only some of which were substantial, carried the action forward. Large sections of the indigenous population at both the Baltic and the Black Sea ends remained in place after the migration process had worked itself out. We are not looking, then, at the transfer of an entire population unit from point A to point B, with added ethnic cleansing. But to gain access to the new wealth of the frontier zone by making Rome shift your group into preferred-partner status in place of another, you did sometimes have to assemble large military forces in order to overturn the existing political order. Unlike today, therefore, migration units had to be both large and heavily armed.
Third, the fact that ambitious kings who wanted to move from the periphery into the frontier zone could not put together forces of sufficient size just from their military retinues explains the other peculiarity of the larger groups involved in the flow: the participation of women and children. The result was a migration flow that took the form neither of wave of advance nor of elite transfer. Small familial groups moving randomly over the landscape would have been mopped up piecemeal by the Carpi, Sarmatians or Rhine–Weser Germani, and kings with their warband-sized retinues could not have won the big battles that needed to be fought.
Aside from offering us an additional migration model that emphasizes the fundamental links between migration and development, the changes that took place in Germanic society in the early Roman era have another dimension: we can discern in them the first glimmers of the overarching process that would eventually even out the massive regional disparities in development characteristic of the European landscape at the beginning of the first millennium. Well beyond those regions that had fallen under direct Roman control, contact with the Empire on every level unleashed forces whose cumulative effect was to transform Germanic society. The result by the fourth century, as we have seen, was that much more substantial political structures had come to hold sway over a much larger population. These forces were felt most intensely close to the frontier, but they had some effects beyond, most obviously because some of the economic networks – those producing amber and slaves, for instance – extended long tendrils. Of still greater importance was the appearance of a richer inner periphery, surrounding the Roman Empire proper, which generated a tendency towards predatory migration into it from the regions beyond. Thus, much more than a thin client strip around Rome’s European frontiers now fell within range of wider-ranging processes of transformation that would eventually undermine the Mediterranean’s dominion. Even by the late Roman period, however, vast areas of east-central and eastern Europe remained unaffected. This would change when the new political order of client states created by the second-and third-century migration flows was thrown into tumult in the later fourth century. And if migration had so far played a secondary role to development that too was about to change. The era of the Huns had begun.