The Roman Empire reached its greatest extent around 115 A.D. The enormous area and the innumerable languages , cults and customs apparently exceeded the dimensions of what it was possible to maintain as a whole . The tribes immigrating from the north-east , revolt against uniformity , but also internal power struggles led to an incessant sequence of wars and insurrections subjecting the economic and social structures to hard endurance tests . The Greek eastern half , which had come to the empire relatively late and was economically stronger , was better able to stand these problems than the West ; by means of fundamental reforms it succeeded in reviving state unity several times . This ability to create something new from ruins , reviving what had been earlier in form and its conception of itself , is the fascinating aspect of Byzantine history . The conservative trait , which is so especially noticeable for us in Byzantine art , should not mislead us about the profound changes . It was the strength for creative adjustment to completely changed conditions which made it possible to build up a tradition . The link with the idea of the Roman state was preserved visibly in the Greek form of the word 'Roman' . The Byzantines described themselves as 'Rhomaioi' . Never was the idea of restoring The Roman Empire as a whole completely abandoned . Even in times of the greatest difficulties , it was the ideal of Byzantine policy .

The continuation of the notion of the Roman state makes it impossible to state clearly from when the Byzantine Empire existed . From a legal point of view , the continuity of the Roman Empire , until Byzantium ceased to exist , is clear . But , in keeping with historical reality , sometime between the laying of the foundation stone for Constantinople and the revival of the Empire's fortunes under Herakleios , the changes had reached such an extent that the Classical Imperium had become a Medieval Empire .

One of the decisive events on this way was the division of the Mediterranean area by Islam . At almost the same time , the West made itself independent , a process which led to a first major stir with the crowning of Charlemagne as emperor . Out of the confusion of the migration of the peoples and the buried Roman tradition in Europe grew a third centre of power , religiously different despite the profession of Christianity , that initially adopted culturally decisive impulses from the East . However , the constant struggle for the claim to leadership opened up intellectual rifts which were scarcely less deep and dangerous than those of Islam . The third important factor for Byzantium was the advance of the Slavs into the Balkans . After the main wave of the migration of the people had already ebbed away , they pushed forward like a wedge between the Greek East and the Latin West ; a process which also fell in the period between the 7th. and 9th. centuries . The Slavonic occupation and settlement of the land is one of the reasons why the Islamic expansion was not experienced as a common threat to the West and defence was not coordinated . The changes forced fundamental changes onto the Byzantine administration and army that represented the main support for the emperor against claims of the land-owning aristocracy which were tearing the Empire apart . So long as it was possible to maintain a balance between these forces , however tricky , Byzantium remained a great power .

There are two decisions dating back to Constantine the Great to which Byzantine history owes its continuity to a considerable extent . The first one concerns the choice of a new capital . Constantine raised the old Greek city of Byzantion to the seat of government which was solemnly consecrated as the city of Jesus Christ on 11 May 330 . And that already touches on the second decision : the link with Christianity which began under Constantine . The anchoring of the emperor's absolute rule in the universal religion , the legitimisation of the one emperor through the one God created an ideal basis for the coherence of the Empire .

At the same time , the unity of Christendom became a central problem for the state . It affected government power so directly that the pressing problems of the young religion could not be left just to the ecclesiastics . But the imperial interventions often only settled the conflicts in a rough and ready way ; at times they even fomented them . This is true especially for the North African and Middle Eastern parts of the Empire with the oldest episcopal sees , Jerusalem , Alexandria and Antioch , which claimed the power to decide on matters concerning the faith for themselves and did not always back council resolutions from the capital . The difference in opinions between Oriental and Greek territories remained virulent until the Arab conquest , also promoting the latter .

In addition to internal church disputes , Imperial decrees also regulated the suppression of paganism . Whereas the followers of Jesus of Nazareth had been subject to persecutions until the recognition of Christianity , now things changed . Between 319 and 435 , again and again ever sharper laws were promulgated against the pagans and the exercise of the ancient cults . There were anti-pagan riots in the 5th. century even systematic persecutions . On the other hand , numerous ancient customs and opinions found their way into Christian rites . The victory of the new religion was a protracted , tough process which dragged on for many generations and had still not been completed even in the 6th. and 7th. centuries .

After the fall of the western Roman Empire , the new capital had no competitors ; created as capital of a state already in existence , it developed , unlike European capitals , independently of its hinterland . This fabulously rich metropolis with the imperial palace , the aristocrats' houses and the often concealed luxury of its merchants and officials admittedly contained enough social explosive to endanger even the emperor's position from time to time .

At first glance , a brilliant start , at a second , however , the seed of the deep crisis of the 7th. century , is the to a large extent successful restoration of the Roman Empire as a whole under Justinian I . He was able to build on the consolidation of the state finances under his predecessors , he quelled an uprising by the lower classes in Constantinople and made peace with the Persians who had been threatening the eastern frontier for centuries . After that , he concentrated all his forces on the subjection of the Teutonic kingdoms in Italy , Spain and North Africa which did , it is true , nominally acknowledge East Roman supremacy , but did not , however , want anything to do with an actual dominance by Byzantium .