The zenith of the Byzantine Empire was reached in the middle of the sixth century during the reign of the Emperor Justinian (527-565). The internal stabilization of the Byzantine state was completed, and Justinian then embarked on a wide range of external re-conquests. Justinian's prime directive was to restore the Roman Empire to its former glory in the west. He sought to strengthen the immutable law that Byzantium, the successor of Rome, maintained not only in the east but also the west, and by doing so, he hoped to revive the unity of the Roman world. In addition to attempting to conquer Italy and restore all the old dominions of the Roman Empire, Justinian also had to quell inner unrest by fighting barbarian usurpers, securing the borders, re-establishing religious orthodoxy, reorganizing the law, and reviving prosperity.

Accounts describe him as a stocky and ugly man, but he was deeply conscious of the prerogatives and duties of his position as a person exalted and close to God, and he was self-controlled in his personal life. From an administrative standpoint, he was an adroit diplomat and organizer who was gifted when it came to choosing collaborators and streamlining the administration of his empire. He was also married to Theodora, a woman of extraordinary beauty, courage, and intellect.

Justinian was profoundly religious, which ensured that he spent considerable time attempting to reestablish orthodoxy and guide the church into the future. Justinian even ensured religious uniformity as this was the same as domestic law. There was no real separation between the legal order and canon law.