page_title: State church of the Roman Empire
section_title: Expansion of Christianity in Europe
hierarchical_section_title: State church of the Roman Empire / History / Expansion of Christianity in Europe
caption_attribution_description: English: Small map from plate 23 of Professor G. Droysens Allgemeiner Historischer Handatlas, published by R. Andrée.
context_page_description: With the Edict of Thessalonica in 380 AD, Emperor Theodosius I made Nicene Christianity the Empire's state religion. The Eastern Orthodox Church, Oriental Orthodoxy, and the Catholic Church each claim to stand in continuity with the church to which Theodosius granted recognition, but do not look on it as a creation of the Roman Empire.
  Earlier in the 4th century, following the Diocletianic Persecution of 303–313 and the Donatist controversy that arose in consequence, Constantine had convened councils of bishops to define the orthodoxy of the Christian faith, expanding on earlier Christian councils. A series of ecumenical councils convened by successive emperors met during the 4th and 5th centuries, but Christianity continued to suffer rifts and schisms surrounding the issues of Arianism, Nestorianism, and Miaphysitism. In the 5th century, the Western Empire decayed as a polity: invaders sacked Rome in 410 and in 455, and Odoacer, an Arian barbarian warlord, forced Romulus Augustus, the last nominal Western Emperor, to abdicate in 476.
context_section_description: During the 9th century, the Emperor in Constantinople encouraged missionary expeditions to nearby nations including the Muslim caliphate, and the Turkic Khazars. In 862 he sent Saints Cyril and Methodius to Slavic Great Moravia. By then most of the Slavic population of Bulgaria was Christian and Tsar Boris I himself was baptized in 864. Serbia was accounted Christian by about 870. In early 867 Patriarch Photios I of Constantinople wrote that Christianity was accepted by the Kievan Rus', which however was definitively Christianized only at the close of the following century.
  Of these, the Church in Great Moravia chose immediately to link with Rome, not Constantinople: the missionaries sent there sided with the Pope during the Photian Schism (863–867). After decisive victories over the Byzantines at Acheloos and Katasyrtai, Bulgaria declared its Church autocephalous and elevated it to the rank of Patriarchate, an autonomy recognized in 927 by Constantinople, but abolished by Emperor Basil II Bulgaroktonos (the Bulgar-Slayer) after his 1018 conquest of Bulgaria.
  In Serbia, which became an independent kingdom in the early 13th century, Stephen Uroš IV Dušan, after conquering a large part of Byzantine territory in Europe and assuming the title of Tsar, raised the Serbian archbishop to the rank of patriarch in 1346, a rank maintained until after the fall of the Byzantine Empire to the Turks. No Byzantine emperor ever ruled Russian Christianity.
  Expansion of the Church in western and northern Europe began much earlier, with the conversion of the Irish in the 5th century, the Franks at the end of the same century, the Arian Visigoths in Spain soon afterwards, and the English at the end of the 6th century. By the time the Byzantine missions to central and eastern Europe began, Christian western Europe, in spite of losing most of Spain to Islam, encompassed Germany and part of Scandinavia, and, apart from the south of Italy, was independent of the Byzantine Empire and had been almost entirely so for centuries.
  This situation fostered the idea of a universal church linked to no one particular state. Long before the Byzantine Empire came to an end, Poland also, Hungary and other central European peoples were part of a Church that in no way saw itself as the empire's church and that, with the East-West Schism, had even ceased to be in communion with it.
caption: The spread of Christianity in Europe by 1000.
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