Old Church Slavonic is the rare case of a literary language created deliberately, for a specific purpose, at a known moment. In 863 the Byzantine emperor sent two brothers from Thessalonica, Constantine, later monk Cyril, and Methodius, to Great Moravia, whose prince had asked for Christian teachers working in the Slavic tongue rather than Latin. Constantine devised an alphabet, the intricate Glagolitic, fitted precisely to Slavic sounds, and the brothers began translating the Gospel lectionary, the Psalter and the liturgy into the Slavic dialect of their home region.
The mission collided with Frankish clergy who held that worship belonged only in Hebrew, Greek and Latin, a position the brothers fought in Venice and Rome, winning papal approval for the Slavic liturgy. After Methodius died in 885 his disciples were expelled from Moravia and received in Bulgaria, where the schools of Ohrid and Preslav flourished, and where the simpler Cyrillic alphabet, built from Greek letters with Glagolitic supplements, took the mission's name. The canon of Old Church Slavonic proper is a small body of tenth and eleventh century manuscripts, but from that seed grew the first literary culture of the Slavic world, and the alphabet now used from Serbia to Mongolia.