ORB Online Encyclopedia
Overview of Late Antiquity--The Fifth Century
Section 1: The Fifth-Century Transformation
By the year 300, Diocletian and the other Tetrarchs had succeeded, through extraordinary measures, in restoring the Roman empire to approximately the same boundaries it had possessed in A.D. 100. Yet, as we have seen, it was not the same empire. The Roman identity was now diffuse, and not a firm basis for imperial dominion. During the fourth century unity constantly had to be renewed by force. Even so, there neither was nor could be a single imperial court or capital. The empire had become an alliance of emperors, usually related by descent or marriage, who held essentially independent power. "Imperial unity" was their recognition of each others' legitimacy.
After 395, this arrangement slowly ceased to function. Well before 500, there was, once again, a single emperor and a single capital -- not Rome, but Constantinople. Although legally and ideologically the emperor's power was as all-embracing as it had ever been, practically speaking his domains no longer included most of the Latin provinces of Europe and northwestern Africa. These were now ruled by kings who were legally not Romans, but "barbarians," whose power in large part derived from their leadership of a militarized "barbarian" people.
The transformation described above has sometimes been described as the result of "barbarian invasion" or "a migration of peoples." It is wrong, though, to visualize the Roman empire as being overrun by militarily unstoppable forces or large numbers of aggressive immigrants. The Roman empire did suffer invasion several times in the fifth century, and at least one major kingdom was founded through conquest. By and large, however, the devolution of power to "barbarian" kings was the result of an expedient of imperial rule that got out of hand: the use of federates, or non-citizen troops. The federates settled in many parts of the empire were meant to remain peoples apart, to serve as a military resource without ever taking a significant political role. Barbarian power within the Roman system was devised as an antidote to regionalism and civil war among Romans, a force for unity in the emperors' hands. Once, however, a certain amount of power had been delegated to barbarian leaders, it was impossible to keep them from gaining real control over large districts. Romans in the west gradually became aware that, although a Roman emperor still claimed to rule the world, in their own provinces they were no longer the ruling people. The devolution of military power to non-citizens had resulted in "the fall of the Roman empire."
Index, Overview of Late Antiquity.