VI. Chalcedon (the East, 430-681)

By about 430 the Roman Empire had largely been Christianised. While the western half of the Roman Empire, with its capital at Rome, was under attack and soon to fall, the eastern half of the Empire survived and thrived as a Christianised society with Constantinople as its capital. Its most illustrious ruler was Justinian who ruled 527-565 and, during that time, was able to temporarily reclaim lands occupied by Germanic peoples, engage in a building programme (most famously reconstructing the Hagia Sophia after the Nika riot) and codify Roman law. The two-headed eagle of Constantinople represented the "harmony" of the priesthood and the kingdom, the church and state working in tandem. In the East, unlike in the west, this always meant the state had the upper hand (this is sometimes termed "Caesaropapism") with the Emperor possessing divinely ordained power and above the law. After Justinian many of the lands to the west were lost again, although the following century Emperor Heraclius (r. 610-641) was able to hold the Sassinid Empire of Persia bay until the advent of the Islamic caliphate in the seventh century.

During this whole period, the theological "hot topic" in the church was Christology, that is to say, the relationship between the divine and the human in Christ.

The 381 Council of Constantinople had already condemned the teaching of Apollinarius and affirmed that Christ had a human soul, for, as Gregory of Nazianzen had famously said, “the unassumed is the unhealed”.

For a brief period Nestorius served as Archbishop of Constantinople. Nestorius, who had been trained in the Antiochene School of Theodore of Mopsuetia, was perceived as teaching that the eternal Son of God and the man Jesus are in fact two persons joined in union. Thus, the baby in Mary's womb was just a human. This teaching was opposed by Cyril of Alexandria, who proclaimed “one incarnate nature [sic] of the Logos”. The 431 Council of Ephesus proclaimed Mary to be the Theotokos, the Bearer of God, thus affirming Christ as a single person. This decision alienated a party within the church associated with the School of Edessa, which relocated outside the borders of the Empire to Nisibis. The "Church of the East", the Christian church in the Persian Empire, had already proclaimed itself autonomous in 424 headed by a Catholicos with his seat at Seleucia-Ctesiphon. By the end of the fifth century it had adopted the theology of Nestorius. This church was very missionary minded and reached into Central Asia, India, the Mongols and China. The height of its influence was under Catholicos Timothy I (780-823).

Having resolved that Christ is a single person, the next debate surrounded the issue of "nature". Did Christ have one composite divine-human nature, as Eutyches taught? The Patriarch of Rome, Leo the Great, formulated the orthodox answer to the question, speaking of two natures united but distinct from one another. This was the ruling of the 451 Council at Chalcedon. However, the terminology of the ruling alienated the followers of Cyril of Alexandria, who had used the terminology of "one nature". Churches in Egypt (Copts) and Syria (later known as Jacobites) did not accept the ruling of the Council. They are known as the Oriental Orthodox Churches (or "Monophysites"). These churches, both Coptic and Jacobite, engaged in missionary work, covering an area comparable to the work of the Nestorians. A particularly successful Monophysite churchman and missionary was Jacob Baradaeus (578); there was a twin monophysite movement centred in Egypt. By 575 parallel structures of Oriental Orthodox Churches had been set up. The Chalcedonian church strucure remained and was known as the Melkite (i.e. Imperial) church.

While the Nestorians were outside the Empire, the ongoing presence of non-Chalcedonian Monophysites within the Empire was a major concern for the Empire and for the Church. On the one hand the Monophysites engaged in missionary work. On the other hand they represented disunity. Several attempts were made by Emperors to win over the schismatics with formulations they could accept, such as the Henotikon (482), the theological qualifications of Leontius (d. 543) in respect of “enhypostasis”, or the condemnation of the Three Chapters at the Fifth Ecumenical Council (553), but to no avail. A controversial monphysite formulation used in worship in 512, and then withdrawn, was "one of the Trinity was crucified for us". The Fifth Ecumenical Council was more careful in its language: "one of the Holy Trinity suffered in the flesh".

In the seventh century an attempt was made to speak of the "single will" in Christ. This was proclaimed in Imperial edicts, the Ekthesis (638) and the Typos (648). However, Maximus the Confessor and others perceived this compromise to undermine the full humanity and free cooperation of Christ's human nature in redemption - with implications for our participation in salvation. After Emperors and even a Pope (Honorius I) had opposed what become the orthodox position, the church finally ruled in 681 that there are two wills in Christ.

In the eastern tradition, theologians are mystics. As Gregory of Nyssa wrote, “the one who is going to associate intimately with God must go beyond all that is visible and… believe that the divine is there where the understanding does not reach.” Pseudo-Dionysius spoke of God in apophatic terms i.e. in terms of what He is not (rather than what He is); we progress in the knowledge of God as we follow the three-stage path of purification, illumination and union (theosis). Leading lights of eastern monasticism of the age, based in Palestine, were Euthymius the Great and Sabbas the Sanctified. At Sinai, a second centre of monasticism in the fifth and sixth centuries, was John Climacus (d. 649), who wrote the Ladder of Divine Ascent as a sort of 30-step road-map to ascetic growth and achievement. It was he who was one of the first to speak of the practice of inner mental prayer (hesychasm).

During this time the form of Christian public worship also continued to develop and diverge between east and west. The typical form of an eastern church was no longer the Roman-inspired rectangular basilica, but rather the square-shaped martyrium. These buildings were conceived not merely as "meeting houses", but as images of the cosmic order, places of encounter between heaven and earth. The divine liturgy, as public worship was called in the east, took the command "do this in remembrance of me" as a principle for reenacting the drama of salvation. Augustine had written, “All that is beautiful comes from the highest Beauty, which is God.” Christian worship was, correspondingly, aesthetic in character. During the course of the service first the Scriptures and then the elements for Communion were ceremonially brought into the nave. The culmination of the service is the anaphora prayer before Communion, in which the Holy Spirit is invoked (epiclesis) down upon the bread and wine before the worshippers partake. Following the basic two-part structure (liturgy of the Word followed by liturgy of the Eucharist) established in the early Christian centuries, this was further embellished with more elaborate set petitionary prayers (litanies), anaphora (see above) and songs proclaiming doctrine, such as the Trisagion (438), the creed (510) and “Only-Begotten Son” (536). Roman the Melodist (d.556), John of Damascus, Cosma the Melodist (d. 760) and Andrew of Crete were among those who contributed to the development of the divine liturgy.