The book presents data indicating that from ancient times until the very late Middle Ages, the Volga-Oka interfluve was inhabited by Muscovites - a Slavic-speaking people, whose ancestors were Roxolan Scythians and Slavs of Illyrian origin. In the medieval period, they created the Moscow state, on the basis of which the current Russian state then formed. By the end of the Middle Ages, Muscovites completely assimilated with the Rus, which appeared on the territory of future Russia only in the middle of the 9th century. The book examines the meaning of the word "tsar" and shows that Christianity in Russia has existed since Chief Apostolic times