At the time of the Fall of Constantinople to the invading Ottoman Empire in May 1453, Orthodox Christianity was already entrenched in Russia, whose political and de facto religious centre had shifted from Kiev to Moscow. The Russian Church, a part of the Church of Constantinople until the mid-15th century, was granted full independence (autocephaly) and elevated to the rank of Patriarchate in 1589. The Russian political and ecclesiastical elite came to view Moscow as the Third Rome, a legitimate heir to Constantinople and Byzantium.