sentences:  At first, the Byzantine term "autokrator" expressed only the literal meaning of an independent ruler, but in the reign of Ivan IV (1533-1584) it came to imply unlimited (autocratic) rule.In 1547 the Grand Duke Ivan IV was crowned Tsar and thus was recognized - at least by the Russian Orthodox Church - as Emperor.Notably, the hegumen Philotheus of Pskov claimed in 1510 that after Constantinople fell to the Ottoman Empire in 1453, the Russian Tsar remained the only legitimate Orthodox ruler, and that Moscow was the Third Rome, becoming the final lineal successor to Rome and Constantinople, the two centers of Christianity and of the Roman Empires (Western and Eastern) of earlier periods.