In September 2006 Pope Benedict XVI brought Byzantium to the front pages around the world with his citation of a medieval Greek text, employed to make a sharp criticism of Islam. Quoting from a Dialogue written by Emperor Manuel II (1391-1425), he said: "What did the Prophet bring that was new? Only evil and inhuman things such as his command to spread by the sword the faith he preached" - as if Christians had never spread the faith by the sword.

While this attack on Islam was clearly newsworthy, editors were puzzled by the source he had quoted. The Byzantine Emperor Manuel II is not a household name, though he turned out to be a distinguished ruler of a once great empire in its declining years. He had even travelled to Paris and London, as well as living as a vassal of the Ottoman Turks as the balance of forces swung against the Byzantines. A remarkable leader, he is the author of Dialogue with a Persian (ie a Muslim). This is a debate on the relative values of Christianity and Islam written in the last decade of the 14th century, while Manuel was detained by the Sultan Bayezid (1389-1402). He also composed theological treatises, speeches and letters, which reflect his deep friendships and intellectual interests. Through these copious writings he is one of the most literate emperors of Byzantium, devoted to ancient Greek culture while profoundly aware of the political problems of his time.

What was this mysterious empire that was suddenly propelled into the spotlight by the Pope? For more than a millennium before Manuel II's reign, Christian emperors had been ruling in Constantinople. During these long centuries which link the ancient and medieval worlds, Byzantium had developed out of the eastern half of the Roman Empire and grew into a profoundly Christian, cosmopolitan state that withstood attacks by Persians, Avars and Slavs, Arabs, Russians, Turks and Latins. From its inauguration by Constantine the Great in AD 330 to its capture and sack by the Christian forces of the Fourth Crusade in 1204, the capital Constantinople remained unconquered. And even after a 57-year occupation by western crusaders, the Byzantines regained the city in 1261, and held it for two more centuries until the final siege by the Ottoman Sultan Mehmet II in 1453.