Its core territory is the region now called Moravia in the eastern part of the Czech Republic alongside the Morava River, which gave its name to the kingdom. The kingdom saw the rise of the first ever Slavic literary culture in the Old Church Slavonic language as well as the expansion of Christianity after the arrival of St. Cyril and St. Methodius in 863 and the creation of the Glagolitic alphabet, the first alphabet dedicated to a Slavic language. Glagolitic was subsequently replaced by a simpler Cyrillic.