During the sixth and seventh centuries the Byzantine Empire survived waves of attacks, owing to effective military leadership and to fortifications around Constantinople. Byzantine emperors organized and preserved Roman institutions, and the Byzantine Empire survived until 1453. The emperor Justinian oversaw creation of a new uniform code of Roman law. The Byzantines prized education, and because of them many aspects of ancient Greek thought survived to influence the intellectual life of the Muslim world and eventually that of western Europe.

Christianity gained the support of the fourth-century emperors, and the church gradually adopted the Roman system of hierarchical organization. The church possessed able administrators and leaders. Bishops expanded their activities, and in the fifth century the bishops of Rome, taking the title “pope,” began to stress their supremacy over other Christian communities. Monasteries offered opportunities for individuals to develop deeper spiritual devotion and also provided a model of Christian living and places for education and learning. Christian thinkers reinterpreted the classics in a Christian sense, incorporating elements of Greek and Roman philosophy into Christian teachings.

Barbarian groups migrated throughout Europe and Central Asia beginning in the second century. Among barbarians, the basic social unit was the tribe, made up of kin groups and led by a tribal chieftain. Missionaries and priests persuaded pagan and illiterate peoples to accept Christianity by stressing similarities between pagan customs and beliefs and those of Christianity, and introducing the ritual of penance and the veneration of saints. Most barbarian kingdoms were weak and short-lived, though the kingdom of the Franks was relatively more unified and powerful. Rulers first in the Merovingian dynasty, and then in the Carolingian, used military victories, carefully calculated marriage alliances, and the help of the church to enhance their authority. Carolingian government reached the peak of its power under Charlemagne, who brought much of Europe under his authority through military conquest and strategic alliances.