of the Golden Age of medieval Bulgarian culture during which the Cyrillic alphabet was spread by Bulgarian scholars to other Slavic states such as Russia and Serbia. See also Timeline of Christian missions List of oldest church buildings Christianization of the Slavs Saints Cyril and Methodius Old Bulgarian (also called Old Church Slavonic) Early Cyrillic alphabet Cyrillic script Boris I of Bulgaria Glagolitic alphabet Ballshi inscription Notes References Gjuzelev, V., (1988) Medieval Bulgaria, Byzantine Empire, Black Sea, Venice, Genoa (Centre culturel du monde byzantin). Verlag Baier. Bibliography Sullivan, R.E., (1994) Christian Missionary Activity in the Early Middle Ages (Variorum Collected Studies Series). Ashgate Publishing Limited, . Vlasto, A.P., (1970) The Entry of the Slavs into Christendom: an Introduction to the Medieval History of the Slavs. Cambridge University Press. 9th century in Bulgaria Christianity in medieval Macedonia Bulgaria Byzantine Empire–First Bulgarian Empire relations Byzantine Empire–Holy See relations First Bulgarian Empire Golden Age of medieval Bulgarian culture History of Christianity in Bulgaria Medieval Thrace