For 300 years after A.D. 275 the church in the East was occupied with doctrinal controversies—Arianism, Nestorianism, Monophysitism, and Monotheletism. These arguments concerned the manner in which Jesus is both divine and human. Decisions were made at a series of general councils of bishops (see council, ecumenical); at them was composed the Nicene Creed. These centuries saw a series of Christian writers of unequaled influence (the Fathers of the Church): Origen, St. Athanasius, St. Basil the Great, St. Gregory of Nyssa, St. Gregory Nazianzen, St. John Chrysostom, and Theodoret writing in Greek; St. Ambrose, St. Jerome, and St. Augustine writing in Latin. Origen and St. Jerome had a special role in the church's work of determining and preserving the text of the Bible.
From the 3d cent. monasticism was one element of the church. It was first organized by St. Basil. In the West monasticism was central to the missionary work of St. Martin (Gaul, 4th cent.) and St. Patrick (Ireland, 5th cent.). It received definitive shape from St. Benedict and St. Gregory the Great, who thereby generated a mode of life of continuing vitality in the Roman Catholic Church.
German invasions slowed the conversion of Western Europe (e.g., that of England was recommenced in the 6th cent.). Most of the first invaders were converted to Arian Christianity, but the pagan Franks (with Clovis) adopted orthodox Christianity, a fact that probably helped to consolidate their rule. Out of this kingdom came Pepin and Charlemagne, who, by alliance with the papacy and proclamation of an empire (800), charted an ideal of the Middle Ages.