By the sixth century, the Western Roman Empire was defunct. It had been replaced by its Eastern counterpart, the Byzantine Empire with Constantinople as its capital. But their respective churches, suffering the shakiest of relationships, soon saw themselves threatened by a mutual foe, the rapidly spreading Islamic domain.

The Eastern church realized this, at the latest, when in the seventh century the Muslims captured Egypt and other parts of the Byzantine Empire located in North Africa.

The Crusades also increased the East-West tension that had been growing since 1054, when Patriarch Michael Cerularius of the East and Cardinal Humbert of the West mutually excommunicated each other. When the Crusaders replaced the Greek clergymen with Latin bishops in the cities they captured, the East-West schism came down to touch the common folk.

The break between the two churches became complete during the Fourth Crusade when, according to former Anglican Canon of Canterbury Herbert Waddams, Pope Innocent III played “a double game.” On the one hand, the pope was indignant about the sacking of Constantinople. (See box on page 24.) He wrote: “How can the Church of the Greeks be expected to return to devotion to the Apostolic See when it has seen the Latins setting an example of evil and doing the devil’s work so that already, and with good reason, the Greeks hate them worse than dogs.” On the other hand, he readily took advantage of the situation by establishing a Latin kingdom there under a western patriarch.

After two centuries of almost continuous fighting, the Byzantine Empire was so weakened that it was unable to withstand the onslaughts of the Ottoman Turks, who, on May 29, 1453, finally captured Constantinople. The empire had been slashed down not simply by an Islamic sword but by the sword wielded by the empire’s sister church in Rome as well.