The period of the fall of Rome lasts roughly from 200-500 CE and comprises the decomposition of a highly developed civilization in the face of challenges emerging from peoples much more primitive in technological, cultural, linguistic, and even religious terms. These three-hundred years demonstrate, from Britain all the way to the Adriatic Sea, the shift from Roman order to bloody and lawless disorder. Indeed, while the eras of Republican and Classical Imperial Rome were full of revolts, military difficulties, and economic downturns, it is when studying Rome's last generations that we can fully understand the nostalgia that people of the Middle Ages and Renaissance held for the glorious vision of Rome that died along with Marcus Aurelius.
In effect, then, Roman history beginning with Constantine, as the historian Bury puts it, is European Medieval history. By Constantine's time, the historical circumstances that were to mark the years up through 600 and beyond were already in evidence: Barbarian tribes were seeping into Britain and Western European lands; Emperors as semi-deified, withdrawn, and absolutist kings; involuntary peasant labor on lands not their own; personal bonds and personal law beginning to replace impersonal law common to large expanses of territory; and, of course, the Catholic Church, which would provide spiritual and moral direction, as well as temporal leadership and material support, during the darkest times of the early Medieval period.
Looked at differently, the decline period of Roman history constitutes not so much a break, or numerous breaks, from the classical period, but aggravations of preexisting conditions. Under this conception, it is argued that the pressures of encroaching Barbarians amplified already existent systemic problems within Roman politics, and in doing so overburdened the military, bureaucratic, and financial capacities of the Empire. The external pressures the Empire faced uncovered its internal difficulties, and once these problems were evident, the conceptual bond that held together Rome's large population of un-free subjects and semi- and non-literate citizens disappeared. Faced with all of these problems, the Empire simply couldn't cope. For example, Roman leaders had always faced multiple military threats on opposite ends of impossibly long borders. Similarly, in dealing with these and other threats, Roman policy- makers had often followed a pattern of trying to take the road of least resistance, and, after finding that insufficient, having to expend more time and manpower than would have been originally necessary. Yet, they had succeeded. Continuing, Romans were aware of the challenges and dangers of Barbarian incursions from the middle of the first century CE. Domestically speaking, the problem of not having firm principles for the succession of rulers had been apparent to all from before the time of Caesar. Thus, we must always question the helpfulness of 'rise, zenith, and decline' schemes of understanding historical events: the problems that felled the Roman Empire were evident even at its greatest height.
So, what was paradigmatically, drastically different about the late Roman period? If we wished to take the mystery out of it all, we could claim that the fall of the Roman Empire was scripted. First, the empire was too big, and the lanes of communication—in military, food supply, and of course cultural terms—were far too tortuous. To respond to a threat from Parthian Persia, for example, Marcus Aurelius had to remove troops from the Rhine frontier at a time when Barbarians were pushing up against those very borders, and setting in motion the numerous conflict to come. This brings us to the second given of the period: an identifying part of ancient and pre-modern history was the conflict between settled, sedentary, agrarian societies and polities, on the one hand, and nomadic, pastoral, raiding cultures, on the other. The two never coexisted, and could never work out a sustainable symbiosis. Furthermore, the nomads were always attracted to the materials of the settled civilizations, and also wanted to access its culture, though semi- nomadic understandings of sedentary culture were probably quite limited. Thus, this settled-nomadic conflict was bound to affect Rome quite negatively, at the very time when other military threats, and civil war, emerged. One could even ask whether a settled society in the pre-modern world was ever able to defeat nomadic incursions over the very long term, such as Rome faced.
Third, it is important to ponder what Rome was. Conventionally it was a state, and one can locate a reasonably linear decline on the state level. Of course, the Diocletian and Constantine years showed new vitality on the state level, though that vitality changed the polity forever. Still, on the merely political level, Roman decline is clear, and uni-directional. But then, there is the category of Rome as culture and society. Here it is instructive to ask: to what degree were those living within Roman borders Romanized in culture, language, and notions of political order? The answer to this question is impossible to quantify, but it is clear that there was some disjunction between political elites, political structures, cultural elites, and the rest of the masses, which of course outnumbered the elites. What did Rome mean for them, and did that meaning disappear in 476? Roman forms of organization in state and society demonstrated a resilience up until 476 and even after. Emperors in the weakest of times, when the decomposition of the state must have been obvious to all, struggled to maintain Roman form, parlance, and dignity, not as a superficial show, but as a mechanism to provide continuity and logic. More impressively, not only did native Roman leaders and local administrators try to keep up cultural appearances, the Barbarians entering Roman lands also enthusiastically tried to maintain what they thought Rome was. The Barbarian mantra for the period covered in this SparkNote could be: 'we've come to enjoy, not to destroy.' Even Theodoric the Ostrogoth, ruling the Ostrogothic Kingdom of Italy on now defunct Roman lands, maintained Roman political parlance, Latin language, Roman architecture, and Roman hierarchies, even maintaining some relationship with the Eastern Roman Emperor. Pushing the point to its farthest, one could begin to suggest a cultural melding between Roman and German. Of course, the Church and Christianity are added to this mixture, one has what many historians view to be the three pillars of European identity.
What the above suggests, therefore is the following: a) 'decline and fall' is a tricky concept, rendering too superficial our understanding of the final centuries of Rome. Continuities, aggravations of existing conditions, and elements outlasting 'disappearance' are essential to this period of Roman history. b) Roman fall, or at least severe transformation, was made ever-more inevitable as it—a pre-modern, pre-industrial, pre-democratic state—increased in size, and was faced with the settled-nomadic conflict. c) Late Roman history is indistinguishable from early medieval history and the two must be studied together. By providing following generations with Christianity and a political-cultural ideal, the Spirit of Rome pervaded Europe as a whole, continuing to the Renaissance.