Cyrillic script consonants from the older Glagolitic alphabet for sounds not found in Greek. Tradition holds that Cyrillic and Glagolitic were formalized either by Saints Cyril and Methodius who brought Christianity to the southern Slavs, or by their disciples. Paul Cubberley posits that although Cyril may have codified and expanded Glagolitic, it was his students in the First Bulgarian Empire under Tsar Simeon the Great that developed Cyrillic from the Greek letters in the 890s as a more suitable script for church books. Later Cyrillic spread among other Slavic peoples, as well as among non-Slavic Vlachs. Cyrillic and Glagolitic were used for
Saints Cyril and Methodius Saints Cyril and Methodius Saints Cyril and Methodius (826–869, 815–885; ("Kýrillos kaí Methódios"), Old Church Slavonic: Кѷриллъ и Меѳодїи) were two brothers who were Byzantine Christian theologians and Christian missionaries. 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. 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