Peter Frankopan uses new sources to throw fresh light on one of the most written-about events in history, the First Crusade. Frankopan is the first to address the history of the crusade from the point of view of the east, in particular examining the role of the Byzantine Empire and Emperor Alexios I Kommenos. He uncovers close cooperation between Rome and Constantinople and a complex triangular relationship between the west, Byzantium and the Muslim world. And he raises new questions about what provoked western Europe to take up arms in 1096 and why there was a First Crusade at all.

Dr Peter Frankopan is director of the Centre for Byzantine research at Oxford University.