The Byzantine Empire has never had a good press, but few things in its long history have given rise to more controversy than its relations with the crusades. The First Crusade is an epic story, on a par with the tale of Xenophon and the ten thousand. A volunteer army, inspired by a heady mix of greed and piety, marched over 2,000 miles from their homes, fighting their way through eastern Europe and Asia Minor to conquer much of Syria and Palestine. The Byzantine Empire has generally been viewed as a bystander at these extraordinary events, by turns irrelevant and obstructive, but always willing to take the benefit of other people’s heroism. The central figure in the Greek side of the story was Alexios Komnenos, the soldier-emperor who seized power in 1081 and reigned until 1118. ‘I should perhaps compare the emperor Alexius’, wrote Gibbon, ‘to the jackal, who is said to follow the steps, and to devour the leavings, of the lion.’

Hellenophile historians have struggled against this relentlessly negative vision. The French historian Ferdinand Chalandon wrote the first and last serious monograph on the reign of Alexios in 1900. Sir Steven Runciman, whose monumental history of the crusades is still the most widely read work on the subject in English, put