Christianity was established in the First Bulgarian Empire under Boris I in the middle of the 9th century, although it has had its roots in the Balkans since the 1st century and the mission of Apostle Paul. The rise of the Bulgarian Empire made the Bulgarian Orthodox Church autocephalous in 919, becoming the first new Patriarchate to join the initial Pentarchy. The Bulgarian Orthodox Church is the oldest among the Slavic Orthodox churches and has considerably influenced the rest of the Slavic Orthodox world by means of its rich literary and cultural activity in the Middle Ages, as well as by the invention of the Cyrillic script in Bulgaria.