for launching looting-raids into Western Europe. However, Attila's death in 453 brought about the disappearance of the Hunnic empire. In 568, a Turko-Mongol tribal confederacy, the Avars, conducted its invasion into the Middle Danube region. The Avars occupied the lowlands of the Pannonian Plain and established an empire dominating the Carpathian Basin. In 623, the Slavic population living in the western parts of Pannonia seceded from their empire after a revolution led by Samo, a Frankish merchant. After 626, the Avar power started a gradual decline but its reign lasted to 804. Slavic states The Slavic tribes settled in the territory of present-day Slovakia in the fifth century. Western Slovakia was the centre of Samo's empire in the seventh century. A Slavic state known as the Principality of Nitra arose in the eighth century and its ruler Pribina had the first known Christian church of the territory of present-day Slovakia consecrated by 828. Together with neighbouring Moravia, the principality formed the core of the Great Moravian Empire from 833. The high point of this Slavonic empire came with the arrival of Saints Cyril and Methodius in 863, during the reign of Duke Rastislav, and the territorial expansion under King Svätopluk I. Great Moravia (830–before 907) Great Moravia arose around 830 when Mojmír I unified the Slavic tribes settled north of the Danube and extended the Moravian supremacy over them. When Mojmír I endeavoured to secede from the supremacy of the king of East Francia in 846, King Louis the German deposed him and assisted Mojmír's nephew Rastislav (846–870) in acquiring the throne. The new monarch pursued an independent policy: after stopping a Frankish attack in 855, he also sought to weaken the influence of Frankish priests preaching in his realm. Duke Rastislav asked the Byzantine Emperor Michael III to send teachers who would interpret Christianity in the Slavic vernacular. On 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 Svätopluk as