The most militant was the heresy of the Donatists (named after Bishop Donatus), which spread mainly in North Africa in the IV century. the Donatists rebelled against any compromises with the state power, did not recognize bishops and priests who had stained themselves with anything, even in their personal life. As the crisis of the slave-owning Roman Empire worsened, the Donatist movement towards the end of the fourth century. (when the Christian Church became dominant in the Empire) took the form of an open revolt of the poor against the rich: this famous movement of agonists (Christ’s soldiers), or Circumcellions, who with weapons in their hands smashed the estates of the rich. The government had difficulty suppressing the movement, but the Donatist communities in some parts of North Africa persisted until the Muslim conquest (seventh century).

But if the Donatist agonists on dogmatic issues almost did not disagree with the dominant creed and their movement did not create a deep split in the Church, then it turned out differently with the heresy of Arius, the largest opposition movement in the Church of the fourth century, after its transformation into the dominant one. The main focus of Arianism was Egypt, especially Alexandria, where Hellenistic traditions were very strong. Arius was a priest in Alexandria. He did not accept the basic dogma of the official Christian Church about the God-man, according to which God the son is consubstantiated with God the father. According to Arius, Jesus Christ was not born of God, but created by him, therefore, he is not “consubstantiated” with God the father, but “like-minded” with him. The difference between these two words in Greek are expressed in one letter “I”: “ὁμοιούσιος” and “ὁμοούσιος,” but this difference was not extremely important. After all, it was about the nature of Jesus Christ the Savior, and this was the basis of the foundations of the Christian faith. There were heated arguments over Arius ‘ sermon. Aria was supported by a large part of the population of Egypt, especially Alexandria, and it came to street fights.

Behind this, of course, lay political motives: the unwillingness of the inhabitants of Egypt to tolerate the centralizing policy of the Empire. But it was just for the Emperor that it was most important to preserve the unity of the state. The Emperor Constantine, though not yet a Christian himself, took vigorous measures to overcome the schism. He called the Ecumenical Council of the clergy on this occasion (the 1st Ecumenical Council of 325 in Nicaea). The heresy of Arius was condemned, and Arius himself has since been regarded in the Orthodox Church as the most terrible heretic and sinner. However, Arianism still existed for a long time. It spread beyond the borders of the Empire, it was adopted by the Goths, vandals, Lombards, later, however, converted to Catholicism.

Arianism was defeated, but soon appeared close to him the doctrine of Nestorius (Bishop of Constantinople). Nestorius taught that Jesus Christ was a man who was only externally United with the second person of the Trinity — God the son, and that therefore the virgin Mary should not be called the mother of God, but the mother of man or the mother of Christ. Nestorius ‘ heresy was discussed at the 3rd Ecumenical Council of Ephesus (431). Nestorianism was condemned. However, it had a very strong influence in the East, where dualistic religions had long prevailed. In the East, it remained as an independent religion for a long time, it played a major role in medieval Central Asia and is still preserved in some small Nations (aisors, Maronites in Lebanon, “Syrian Christians” in South India).

In the struggle against Arianism and Nestorianism in the IV-V centuries. there was an opposite trend on the same issue of the nature of Jesus Christ. Representatives of this trend taught that Jesus Christ was not really a man, that in him the divine nature so suppressed the human, that Jesus Christ was in the fullest sense of God. It was not two, but one nature — divine. This doctrine of the” one nature ” of Jesus Christ gave rise to the Monophysite (from the Greek (μννος — one, φύσις — nature) sect founded by Bishop Eutychius. It gained widespread influence in the Eastern Roman Empire in the fifth century. Despite its condemnation by the 4th Ecumenical Council of Chalcedon (451), it was strengthened in a number of countries. This showed the struggle of these countries for ecclesiastical and political independence from Byzantium. The Armenian Church, as well as the Copts and Abyssinians, still adhere to Monophysitism.