Only a few decades after Emperor Theodosius I declared Christianity the official religion of the Roman Empire, the Western Empire came to a painful and symbolic end when the Visigoths sacked Rome. Such former Roman strongholds in what are known today as North Africa, Sicily, Italy, France, Spain, and Britain were thrown into political chaos and uncertainty, and the ensuing centuries were characterized by nearly endless warfare and plunder. Against this backdrop, the Western, Latin-speaking church, centered in Rome, expanded into the territories of modern-day Western and Central Europe, and grew in power and influence.
Meanwhile, the Eastern Roman Empire, or Byzantine Empire, continued to enjoy security and wealth. Constantinople served as the political and spiritual center for Greek-speaking Christians whose communities were thriving in Greece, Asia Minor (modern-day Turkey), Palestine, and Egypt. The Christian Byzantine Empire lasted through fluctuating fortunes until the Ottoman conquest in 1453. During these thousand years, the Byzantine church spread north and east from present-day Greece, Turkey, and Hungary, but lost contact with the important religious centers of Antioch, Alexandria, and Jerusalem in the Muslim conquest of the 7th century.
The growth of the monastic movement in the 4th and 5th centuries provided the basis for the missionary efforts of the eastern and western churches. Basil of Caesarea (c. 330-379) wrote rules for monastic living for Greek-speaking monks, which are still followed in Orthodox Christianity. Benedict of Nursia (c. 480-547) wrote the Rule of Benedict for Latin-speaking monks, which is still in use in Benedictine monasteries. These rules sustained strong organizational structures that allowed monks, scribes, and missionaries to travel great distances spreading Christian teachings. In their effort to win converts, monks traveled throughout Europe, building churches and monasteries wherever they went. In some circumstances, the conversion of rulers or generals meant the conversion of peoples or armies. In other circumstances, Christianity permeated the daily life of villages or towns, weaving people together into nations sharing a common language and belief.
Monks of the Eastern Orthodox Church spread north and east from Constantinople. Sts. Cyril and Methodius, remembered as "apostles to the Slavs," took the Christian message to the Slavic peoples in the mid-9th century. In 860, Khan Boris, leader of the Bulgars (a semi-nomadic people in eastern Europe), was baptized. The Byzantine Patriarch sent missionaries to Russia, but their mission ended in 878. A century later, however, Prince Vladimir of Kiev was baptized, and Christianity continued its spread among the diverse tribes in the vast lands of Russia. The Byzantine mission to the Slavs contributed significantly to creating a cultural, linguistic, and political sensibility through which the modern nations of Ukraine, Bulgaria, Russia, and Serbia emerged.
Missionaries from the Western Church traveled north and west from Rome. King Clovis of the Franks (a northern European tribal group) was baptized in 498 at the urging of his Christian wife Clotilde, thus solidifying the influence of the Church in western Europe. While some people groups, like the Celts and the English, converted through marriage and missionary contact, others succumbed to forced conversion. Between 772 and 804, the Frankish King Charlemagne pursued a policy of military conquest followed by the execution of all Saxons (another Germanic tribal group) who refused baptism. The Roman Church's mission to the Germans, Franks, Saxons, Celts, and English provided the foundation for Western Europe's sense of cultural unity.