ael III to send teachers who would interpret Christianity in the Slavic vernacular.
Upon Rastislav's request, two brothers, Byzantine officials and missionaries Saints Cyril and Methodius came in 863. Cyril developed the first Slavic alphabet and translated the Gospel into the Old Church Slavonic language. Rastislav was also preoccupied with the security and administration of his state. Numerous fortified castles built throughout the country are dated to his reign and some of them (e.g., Dowina, sometimes identified with Devín Castle) are also mentioned in connection with Rastislav by Frankish chronicles.
During Rastislav's reign, the Principality of Nitra was given to his nephew Svatopluk as an appanage. The rebellious prince allied himself with the Franks and overthrew his uncle in 870. Similarly to his predecessor, Svatopluk I (871–894) assumed the title of the king (rex). During his reign, the Great Moravian Empire reached its greatest territorial extent, when not only present-day Moravia and Slovakia but also present-day northern and central Hungary, Lower Austria, Bohemia, Silesia, Lusatia, southern Poland and northern Serbia belonged to the empire, but the exact borders of his domains are still disputed by modern authors. Svatopluk also withstood attacks of the semi-nomadic Magyar tribes and the Bulgarian Empire, although sometimes it was he who hired the Magyars when waging war against East Francia.
In 880, Pope John VIII set up an independent ecclesiastical province in Great Moravia with Archbishop Methodius as its head. He also named the German cleric Wiching the Bishop of Nitra.
After the death of King Svatopluk in 894, his sons Mojmír II (894–906?) and Svatopluk II succeeded him as the King of Great Moravia and the Prince of Nitra respectively. However, they started to quarrel for domination of the whole empire. Weakened by an internal conflict as well as by constant warfare with Eastern Francia, Great Moravia lost most
