The Slavs arrived from the East between the 5th and 6th centuries during the Migration Period. As a response to onslaughts by Avars, the local Slavic tribes rebelled and established Samo's Empire (623–658), the first known Slavic political entity. In the 9th century, the castles at Bratislava ''(Brezalauspurc)'' and Devín ''(Dowina)'' were important centres of the Slavic states: the Principality of Nitra and Great Moravia. Scholars have debated the identification as fortresses of the two castles built in Great Moravia, based on linguistic arguments and because of the absence of convincing archaeological evidence.