The reign of Manuel I (1143-1180) marked the high point of the revival of the Byzantine empire under the Comnenian dynasty. It was however followed by a rapid decline, leading to the sack of Constantinople by the Fourth Crusade in 1204. This book, the first devoted to Manuel's reign for over 80 years, reevaluates the emperor and his milieu in the light of recent scholarship. It shows that his foreign policy was a natural response to the Western crusading movement and the expansionism of the German emperor Frederick Barbarossa. It also shows that what he ruled was more than the impoverished rump of a once great empire, or a society whose development had been arrested by a repressive regime. The twelfth century is presented here as a distinctive, creative phase in Byzantine history, when the empire maintained existing traditions and trends while adapting to a changing world.