The brothers also founded an academy, initially led by Methodius, which produced hundreds of Slavic clerics. A well-educated class was essential for administration of all early-feudal states and Great Moravia was no exception. "Vita Methodii" mentions that the bishop of Nitra served as Svatopluk I's chancellor, and even Prince Koceľ of the Balaton Principality was said to have mastered the Glagolitic script. The location of the Great Moravian academy has not been identified, but possible sites include Mikulčice (where some styli have been found in an ecclesiastical building), Devín Castle (with a building identified as a probable school), and Nitra (with its Episcopal basilica and monastery). When Methodius’ disciples were expelled from Great Moravia by Svatopluk I in 885, they disseminated their knowledge (including the Glagolitic script) to other Slavic countries, such as Bulgaria, Croatia, and Bohemia. They created the Cyrillic script, which became the standard alphabet in the Kievan Rus' (modern day Russia, Ukraine and Belarus). The Great Moravian cultural heritage survived in Bulgarian seminaries, paving the way for the Christianization of Kievan Rus'.