In the 9th century, the Byzantine state was very engaged into the cultural and religious expansion among the newly settled people in the Balkans. In 864 they finally succeeded into Christianizing the Bulgarians, thus including them into their cultural sphere. Especially important for the history of the Serbian culture was the missionary work of Saints Cyril and Methodius which operated in Great Moravia since 863, introducing the original, Slavic alphabet and translating Byzantine religious and political works. This was the foundation of the Slavic literacy and literature, which soon profoundly influenced the Serbs, leaving major mark in their tradition and culture.