Old Church Slavonic language, Slavic language based primarily on the Macedonian (South Slavic) dialects around Thessalonica (Thessaloníki). It was used in the 9th century by the missionaries Saints Cyril and Methodius, who were natives of Thessalonica, for preaching to the Moravian Slavs and for translating the Bible into Slavic. Old Church Slavonic was the first Slavic literary language and was written in two alphabets known as Glagolitic and Cyrillic (the invention of Glagolitic has been ascribed to St. Cyril). Old Church Slavonic was readily adopted in other Slavic regions, where, with local modifications, it remained the religious and literary language of Orthodox Slavs throughout the Middle Ages. [Britannica]
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