They evangelized to the Slavic peoples, translated the liturgy into Slavonic and made numerous converts. They are also credited with devising and spreading the Glagolitic alphabet, which was used for Slavonic manuscripts before the development of the Cyrillic, the alphabet derived from Glagolitic, that, with small modifications, is still used in a number of Slavic languages.
They promoted Christianity among Slavic peoples by translating liturgy into Slavonic and gaining numerous followers. They are recognized for developing and disseminating the Glagolitic script, which was used for Slavonic manuscripts before Cyrillic, an alphabet derived from Glagolitic that is still utilized in some Slavic languages.