or Čingov. The lack of written sources does not allow to finally conclude if these events were caused by internal changes or by Moravian expansion. Pribina could be a ruler of an independent unity (Principality of Nitra) or in the case that Moravian expansion preceded his expulsion, he was a member of "Moravian" aristocracy. Other historians write that Pribina's Nitrava cannot be identified with Nitra. Charles Bowlus says that a letter, written by Theotmar, Archbishop of Salzburg and his suffragan bishops in about 900, strongly suggests that Nitra was only conquered by Svatopluk I of Moravia only in the 870s. However, according to Třeštík, this information can be explained as a reasonable mistake of the Frankish bishops who knew that the territory was in the past a separate "regnum" different from Moravia and because it was ruled by Svatopluk I, they incorrectly assumed that he also conquered it. According to archaeologist Béla Miklós Szőke, no source substantiates either the theory that Pribina was the head of an independent polity or the identification of Nitrava with Nitra. Richard Marsina writes that the Slovak nation emerged in that principality during Pribina's reign. Regarding the 9th century, the archaeological researches successfully established a distinction between "9th-century Slavic-Moravian" and "steppe" burial horizons in Slovakia. Great Moravia Moravia emerged along the borders of the Avars' territory. 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 influence of Frankish priests preaching in his realm. Rastislav asked the Byzantine Emperor Michael 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 Old Church Slavonic. 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 - Devín Castle) are also mentioned in connection with Rastislav by Frankish chronicles. During Rastislav's reign, the