East and West: The Great Schism and Eastern Orthodoxy

Over centuries, Christianity in the Greek-speaking East and Latin-speaking West grew apart. Disagreements included the authority of the pope, whom Western Christians saw as head of the whole church while Eastern Christians saw him as first among equal patriarchs; the 'filioque' phrase added in the West to the Nicene Creed; and differences in practice such as leavened or unleavened bread. In 1054 papal legates and the Patriarch of Constantinople excommunicated each other, an event remembered as the Great Schism, though the split hardened gradually.

The Fourth Crusade's sack of Constantinople in 1204 deepened Eastern bitterness. Eastern Orthodoxy developed a distinctive tradition centered on the liturgy, icons, the monasteries of Mount Athos and self-governing national churches in Greece, Russia, Serbia and elsewhere. In 1965 Pope Paul VI and Patriarch Athenagoras lifted the mutual excommunications, though the churches remain separate.