Rus state, founded by Oleg of the Ryurik dynasty when he moved his capital from Novgorod to Kiev in about 882. Under Igor (913-45) and Svyatoslav I (r.945-72) Kievan control extended from the Gulf of Finland to the Black Sea. The Kievan state adopted Orthodox Christianity in 987, forging close cultural and political links with the Byzantine empire which had a formative effect on early Russian culture. Kievan Rus broke up into several principalities in 1132, though all were nominally subject to the prince of Kiev. The principality was overrun in 1240 by the Mongols.