"The Byzantine Empire survived nearly a millennium longer than its Western ancestor"

The former Hagia Sophia cathedral, built in the 6th century

The end came in 1453 with the fall of Constantinople to the Turks.

Four centuries earlier, Christian brother had broken with Christian brother: the Church of the East and of the West hurled bitter anathemas at each other (the Schism of 1054, which has never been resolved). 

After the Turks overran much of Asia Minor (1071), the Eastern emperor did appeal to Rome for military assistance.  So, the pope – Urban II – called the First Crusade (1095); but as the western warriors approached Constantinople on their way to the Holy Land, they must have felt like shabby country cousins.  They were absolutely stunned by the fabulous wealth and advanced culture of the Eastern empire.

The schism deepened with the Massacre of the Latins (1182), in which much of the Roman Catholic portion of the imperial capital was wiped out.

The event that permanently crippled the Byzantine Empire was the bloody retribution of the Fourth Crusade – in which the Frankish crusaders, sailing from Venice, sacked and burned Constantinople (1204).  Thousands of Eastern Christians were butchered.

[The Imperial Library, last of the great ancient libraries, was almost completely destroyed.

This is the crusade in which the warriors looted such items as the bronze horses that were carted back to grace the cathedral in Venice.

The illustrious Venetian traveller, Marco Polo, was born fifty years after the Fourth Crusade].

With the collapse of the Byzantine Empire in the 15th century, the center of Orthodox Christianity shifted to Moscow and the Russian Empire.