While Greek Christians called their church and religion Orthodox, Latin Christians adopted the term Catholic (from catholicus, “universal”). The term catholic Christianity was originally used to authenticate a normative, orthodox Christian cult (system of religious belief and ritual) on the grounds of its universality and to characterize different beliefs and practices as heterodox on the grounds that they were merely local and did not reflect duration, unanimity, or universality. These three characteristics of Latin orthodoxy were defined by the 5th-century monastic writer Vincent of Lérins (died c. 450) and adopted generally throughout the Latin church.
Devotional movements that differed from the norms of orthodoxy were defined as heterodoxy, or heresy. The earliest of these were several forms of Judaizing Christianity and Gnosticism, a dualist belief in asceticism and spiritual enlightenment. Once Christianity was established throughout the empire, other local movements were also condemned. Donatism, the belief among many North African Christians that Christian leaders who had bowed to pagan imperial persecution before 313 had lost their priestly status and needed to be reordained, was the first major heterodox practice to be considered—and condemned—at an imperial church council (411). Other movements were Arianism, which challenged the divinity of Jesus, and Pelagianism, which denied original sin and emphasized purely human abilities to achieve salvation. Other beliefs, usually those that contradicted increasingly normative doctrines of Trinitarianism (the belief that the Godhead includes three coequal, coeternal, and consubstantial persons) or Christology (the interpretation of the nature of Christ), were also condemned as heresy.
Normative Christianity, which was expressed in imperial legislation, church councils, and the works of influential Christian writers, gradually became the faith of Europe’s new regional rulers. Within that broad, universal ideology, however, many of the new kings and peoples based their claims to legitimacy and a common identity on their own versions of Latin Christianity, as expressed in local law, ritual, saints’ cults, sacred spaces and shrines, and saints’ relics. The cults of saints and their relics served to territorialize devotion, and control over them was a distinctive sign of legitimate power. Although the older empire and the new, nonimperial lands in Europe into which a new culture expanded came to call themselves Christianitas (“Christendom”), they were in practice divided into many self-contained entities that have been called “micro-Christendoms,” each based on the devotional identity of king, clerics, and people. Kings and peoples
The kings of new peoples ruled as much in Roman style as they could, issuing laws written in Latin for their own peoples and their Roman subjects and striking coins that imitated imperial coinage. They also sponsored the composition of “ethnic” and genealogical histories that attributed to themselves and their peoples, however recently assembled, an identity and antiquity rivaling that of Rome. Although the Romans, who called their own society a populus (“civil people”), used the term rex (“king”) only for rulers of peoples at lower levels of sociocultural development, the political order of kings and peoples became a commonplace in Europe in late antiquity and would remain so until the 19th century. Some of these kingdoms, especially that of the Visigoths in southern Gaul and later in Iberia, also modeled themselves on the ancient Hebrew kingdoms as described in Scripture. They borrowed and adapted some ancient Jewish rituals, such as liturgically anointing the ruler with oil and reminding him in sermons, prayers, and meetings of church councils that he was God’s servant, with spiritual and political responsibilities that legitimized his power.
As the cultures associated with the new kings and peoples spread throughout western Europe from the 5th to the 8th centuries, they influenced political and religious change in areas that the empire had never ruled—initially Ireland, then northern Britain, the lower Rhineland, and trans-Rhenish Europe (the lands east of the Rhine River). The bishop and the monk were two of the most remarkable and longest enduring religious and social inventions of late antiquity; the barbarian kingdoms were a third. Although many of the latter did not survive, their experiments in Christian kingship, as represented in texts, ritual, pictures, and objects, began a long tradition in European political life and thought. The great commission
The process of expansion was also driven by a missionary mandate. Reflecting a new, literal, and personal understanding of Jesus’ command in the Gospels to baptize and to proclaim the word of God (Matthew 28:19; Mark 16:15), the work of conversion to Christianity was extended to all peoples, not just to those of the empire. Conversion was carried out at first by individual Christians acting on their own, not as agents of an organized church. Greek Christians from Constantinople also undertook missionary work, sometimes individually but also as an increasingly prominent aspect of Byzantine imperial diplomacy in the Balkans and north of the Danube valley and the Black Sea. In the eastern parts of the Byzantine Empire, communities of Nestorian Christians, who stressed the independence of the human and divine persons of Christ, moved beyond the imperial frontiers, first into Persia and then farther east. By the 10th century a long string of such settlements ran along the Silk Road from the Mediterranean to China.
Individual conversion stories were modeled on that of St. Paul the Apostle (Acts of the Apostles 9–10), which itself was echoed in the Confessions of St. Augustine. Individual conversion experiences touched people in all walks of life: Martin of Tours, the soldier turned ascetic and bishop; the Gallo-Roman aristocrats Sulpicius Severus—who wrote the influential life of Martin—and Caesarius of Arles; and the free Romano-Briton St. Patrick, who had been a slave in pagan Ireland and returned to convert his former captors.
But the most widely accepted model of conversion of both religious belief and practice was collective—that of a ruler and his followers together as a new Christian people. In this way, the king and church integrated rulership with clerical teaching and the development of the liturgy and with the definition of sacred space, control of sanctity, and the rituals surrounding key moments in human life, from baptism to death and burial. The most notable of the collective conversions were that of the Visigoths from Arian to Catholic Christianity in 589, that of the Frankish leader Clovis by his Catholic Burgundian wife Clotilda and the Gallo-Roman bishop Remigius of Reims about the turn of the 6th century, and that of Aethelberht of Kent by St. Augustine of Canterbury.
As Romans and non-Romans locally assimilated into new peoples during the 6th and 7th centuries, non-Romans, as had Romans before them, became Christian monks, higher clergy, and sometimes saints. In the late 5th century the conversion of Ireland, the first Christianized territory that had never been part of the Roman Empire, brought the particularly Irish ascetic practice of self-exile to bear on missionary work. In the 6th century the Irish monk Columba (c. 521–597) exiled himself to the island of Iona, from which he began to convert the peoples of southwestern Scotland. Other Irish monk-exiles moved through the Rhine valley, Austria, Bavaria, Switzerland, and northern Italy. Columban (c. 543–615), the most influential of these missionaries, greatly reformed the devotional life of the Frankish nobility and founded monasteries at Sankt Gallen, Luxeuil, and Bobbio. Irish and Scottish devotional practices also influenced England, where Celtic forms of Christianity clashed with Continental, especially Roman, forms—a conflict resolved at the Synod of Whitby in 664, when Roman norms were adopted first for the kingdom of Northumbria and later for other English kingdoms. Irish influence remained strong in the English church, however, especially in matters of learning, church reform, missionary exile, and clerical organization.