Defining the years from 300-1000 CE as "The Early Middle Ages" indicates, more than anything else, the perspective of modern historians and Renaissance writers who looked back with disgust on the disorder and inelegance of preceding years. Writing in a time of arguably secular societies and unitary states, historians have tried to understand as "middle" the near millennium of time in between the demise of the Roman state, valued for its political centralism, security, technological advances, territorial spread, and legal systems--all those things that comprised a Pax-Romana--and the first hints of increased international trade, unitary states, and cultural-linguistic identities centering on Europe as a whole. While this "middle" conception is helpful in reminding us of discontinuities between the post Constantine era in European History and Europe after 1500, we must remember that the medieval era also manifests continuities with the Roman times. In other words, the "middle" ages were a transformation of institutions and dynamics of Rome far more than a complete break from the past. To cite just a few examples: the great Barbarian invasions instrumental in Roman demise and Byzantine emergence were preceded by dynamics reaching back to the time before the emperor Marcus Aurelius (161-180) (arguably, Goths, Franks, and others entered Gaul to share Roman civilization, and not to destroy it); Christianity, a defining aspect of Medieval Europe, had begun to elaborate theology and hierarchy during the Roman period; Law, to the extent that it emerged from 300- 1000, took as its model the Justinian, Roman compilation.
In the same way, inasmuch as the Middle Ages were transitional, the Early Middle Ages presented similar characteristics to those of the half-millennium succeeding it. The struggle with Islam, and growing commercial interaction with and cultural imaginings about that new confessional civilization around the southern shores of the Mediterranean were well under way by 1000. Defining themselves in terms of dichotomies of Christendom vs. pagan (including Islam) or civilized vs. Barbarian, Europeans scored notable successes against Muslims; though the Crusades are a High Middle Ages phenomenon, its solid military and ideological foundations were laid in the tenth century with the Spanish Reconquista, which itself flourished into the fifteenth century. Similarly, monasticism, of prime importance to high Medieval society, had seen its first few cycles of efflorescence by the 940s, just as the papacy had made serious progress in asserting temporal authority from Northeastern Iberia to Germanic lands. In the socio-economic realm, feudalism, which defined the character of societal relations on all levels at least until Machiavelli's time, crystallized in the ninth century. The Italian city-states that acted as the motor of international trade in the 11-16th century had their start in the tenth century. Byzantine civilization epitomizes the dynamic: emerging fully within the Roman milieu of the 4th century, its life stretched into the cusp of the early modern period of the mid-15th century.
The question that presents itself, therefore, is: when did the Middle Ages begin? A Romanist perspective would dictate that we put Medieval origins in the generation starting with Diocletian and ending with Constantine's death, a period when administrative, political, and ideological bases of the state were so altered as to make it firmly different from the "classical" Roman Empire. This suggests a mid-fourth-century origin. Others could put it a little later, when Theodosius declared Christianity to be the state-supported religion, thereby eclipsing paganism and ushering in another Medieval (and modern) concept of European historyoppression of Jews and other confessional out-groups. Still in the political, Romanist perspective, one could locate the end of Roman history and the beginning of medieval history between the first and second sack of Rome, 410-455, after which the Eastern Roman remainder emerged as the Byzantine state. A demographic historian would put the date earlier, with the 2nd-6th century floods of barbarians into Roman realms. A Church historian would focus on the crystallization of Christian theology, elaboration of Catholic hierarchy culminating in the Roman archbishopric (the Papacy), as well as monasticism and conversion. For that matter, the entry of Islam onto the European consciousness would seem to some as the defining break with classical Mediterranean civilization. Once quite a defensible position, such a view emphasized a disruption in Mediterranean trade patterns and a shift in political balance to the north. Thus, the safest, most functionally sound approach appears to be to commence the narrative from the 450s, bearing in mind that the entire period presents fluid dynamics, and that Europe's medieval story really begins with transformations of the Roman Empire under Diocletian.
Having said this, the dominant aspects of the early Middle Ages are:
1. The establishment of a Christian commonality in self-conscious continuation of the Roman legacy in spite of socio-political fragmentation. This is basically a religious world-view uniting all converted Europeans in the midst of short-lived polities and feudal relations.
2. Antagonistic yet mutually invigorating interaction between Christendom and the Islamic world.
3. Byzantium as battlefield and standard-bearer in the East-West conflict,even as it articulated its own cultural, political, and Christian expression.
4. A contraction of material possibilities in comparison to the Roman era and the reestablishment of scaled-back inter-regional commercial interaction.