Church Slavonic is a historical Slavic language that originated in the 9th century. It was developed by the brothers Saints Cyril and Methodius to translate the Bible and other religious texts for the Slavic peoples. This language played a crucial role in the spread of Christianity in Eastern Europe. Over time, Church Slavonic became the liturgical language of the Eastern Orthodox Church and some Eastern Catholic Churches. While it is no longer spoken as a native language, it is still used in religious services and has influenced many modern Slavic languages.