Under Justinian a policy designed to reconcile the monophysites (those who believed Christ had only one nature) to Chalcedonian orthodoxy was pursued – the Council of Chalcedon definitely defined that Christ has two natures – He is God and Man, one not overcoming the other). Leontius of Byzantium elaborated the view that while the humanity of Christ had no hypostasis, or center of personal being, of its own, it found its center in the hypostasis of the divine Word: it was enhypostatic. The Fifth Ecumenical Council in 553, held in Constantinople, gave its authority to   Leontius’ teaching. At the same time it condemned aspects of the teaching of Theodore of Mopsuestia, Theodoret, and Ibas of Edessa, whose followers had     protested against Leontius’ doctrine, and so finally divided the East Syrian Christians of Persian Mesopotamia from the Byzantine Church. Their Church of the East was called Nestorian by the orthodox.

At the same time monophysites began to form separate churches, both within the Empire and outside its frontiers: the independent existence of the Coptic and Syrian Churches dates from the period. The imperial authorities attempted to find a basis for reconciliation by suggesting that, though there may be two natures, there is only one energy in Jesus Christ, both human and divine. But monoenergism was unacceptable to the strict Chalcedonians, as too was the monothelete doctrine (only one will) that developed out of the controversy surrounding it. Maximus the Confessor was, with Patriarch Sophronius of Jerusalem, one of their leaders in       resisting imperial attempts to force the doctrine of one will in Christ on the Church of the Empire. It was for refusing to obey the imperial edict of 648 forbidding all discussion of the matter while leaving the doctrinal issue unresolved that Maximnus suffered first exile and then the amputation of his tongue and right hand. Meanwhile he spent some time in Rome, where he helped to formulate the doctrine of two operations and two wills in Christ, which eventually received the approval of the Sixth Ecumenical Council (680) of Constantinople.

In the course of the fifth century a number of churches were built in Constantinople. Sufficient has been discovered by archeologists about three of them to provide some idea of their interior layout. Their general plan was similar to that of the original fourth-century Hagia Sofia.

The structure of the church building, during the early years of the development of the Liturgy, influenced the structure of the Liturgy. The structure of the Liturgy also influenced the architecture of the church buildings. It is this interplay between the two that has resulted in the traditional architecture of Byzantine church buildings and the Liturgy itself.