The gradual disappearance of Roman political authority from the Western Empire strengthened the temporal power of the bishop of Rome. In the Byzantine Empire the patriarch of Constantinople remained under the political control of the Christian emperor. Cultural, political, philosophical, and theological differences strained relations between the two cities, and in 1054 the papal legate and the patriarch of Constantinople excommunicated each other.
One reflection of growing difficulties lay in counterclaims to pursue mission in and hold the allegiance of border areas between the two jurisdictions. Rostislav of Great Moravia sought help from the emperor, who (presumably through the patriarch) in about 862 sent two brothers, Constantine (later called Cyril; c. 827–869) and Methodius (c. 825–884), from Constantinople to Moravia. They provided Scriptures and liturgy in the mother tongue of each people evangelized and trained others in their methods. This missionary competition was repeated in Bulgaria when its khan, Boris I, sought to convert to Christianity. Receiving missionaries from both Rome and Constantinople, Boris ultimately accepted the jurisdiction of the patriarch in Constantinople for the church in Bulgaria.
Constantinople’s greatest mission outreach was to areas that later became Russia. In the 10th century the Scandinavian Rus controlled the areas around Kiev. Undoubtedly influenced by his Christian grandmother Olga and by a proposed marriage alliance with the Byzantine imperial family, Vladimir I (c. 956–1015) of Kiev, from among several options, chose the Byzantine rite. Baptized in 988, he led the Kievans to Christianity. His son Yaroslav encouraged translations and built monasteries.
From 1240, and for the next 200 years, the Mongol Golden Horde was suzerain over Russia but generally allowed freedom to the church. For Russians the church proved to be the one means through which they could express national unity. They moved the metropolitanate from Kiev to Moscow, and their church became and remained the largest of the Orthodox bodies, protector and leader for the others. When Constantinople fell to the Ottoman Turks in 1453, Moscow became “the third Rome” and accepted for itself the mystique, dynamism, and messianic destiny of the first Rome—a reality essential to understanding Russian Orthodoxy and nationalism.
East of the Euphrates River, Nestorians and Jacobites maintained headquarters in Persia for eastern outreach. The more numerous Nestorians developed a far-flung mission network throughout Central Asia. The Persian bishop A-lo-pen reached China’s capital, Ch’ang-an (modern Xi’an), in 635 and founded monasteries to spread the Christian faith. By the end of the Tang dynasty (618–907), however, the Nestorian community had disappeared.
In 1289 the pope—responding to a request made 20 years earlier by Kublai Khan that 100 Christian scholars be brought by the Polo brothers to China—sent one Franciscan, Giovanni da Montecorvino (1247–1328). He reached Dadu (modern Beijing) in 1294 and launched a small but successful mission. In 1342 Giovanni dei Marignolli arrived with 32 other missionaries, but their work flourished for less than 25 years because the succeeding Ming dynasty excluded foreigners. Twice Christianity had entered and disappeared from China.
The rise of Islam
Between Muhammad’s death in 632 and the defeat of Muslim forces at Poitiers by Charles Martel’s Franks in 732, Arab Muslims had taken the Middle East and Egypt, then swept across North Africa, turned northward through Spain, and ventured briefly into southwestern France. Within a century Islam had taken control of more than half of Christendom.
The Iberian reconquest, which began as a traditional war of conquest, became a crusade against Islam and fused an Iberian Catholicism that Spain and Portugal later transplanted around the globe. In the early 21st century its members represented nearly half the world’s Roman Catholics. The Crusades (1095–1396) produced among many Christians an adversarial approach to those of other faiths. Ramon Llull (c. 1235–1316) pursued a different way. He studied Arabic and sought through dialogue and reason the conversion of Muslims and Jews.
As a result of the second great transition the faith of the Mediterranean world had become that of all Europe and had largely created its civilization. Christendom had lost half of its territory to Islam, but Europe had become the new centre of the Christian faith.