Saints Cyril and Methodius (Greek: Κύριλλος καὶ Μεθόδιος, Old Church Slavonic: Кѷриллъ и Меѳодїи^[more]) were Byzantine Greek brothers born in Thessaloniki in the 9th century.^{[3][4][5][6][7][8][9][10]} They were Christian missionaries among the Slavic peoples of the First Bulgarian Empire, Great Moravia, and Pannonia. Through their work they influenced the cultural development of all Slavs, for which they received the title "Apostles to the Slavs". They are credited with devising the Glagolitic alphabet, the first alphabet used to transcribe Old Church Slavonic.^[11] After their deaths, their pupils continued their missionary work among other Slavs. Both brothers are venerated in the Orthodox Church as saints with the title of "equal-to-apostles". In 1880, Pope Leo XIII introduced their feast into the calendar of the Roman Catholic Church. In 1980, Pope John Paul II declared them co-patron saints of Europe, together with Benedict of Nursia.^[12]

The two brothers were born in Thessaloniki – Cyril in 827–828 and Methodius in 815–820. Cyril was reputedly the youngest of seven brothers; he was born Constantine,^[13] but took the name Cyril upon becoming a monk shortly before his death,^[14][15][16] according to the "Vita Cyrilli" ("The Life of Cyril"). Their father was Leo, a droungarios of the Byzantine theme of Thessaloniki, and their mother was Maria, who may have been a Slav.^[17]