between the death of Alexios I and the establishment of the Latin empire of Constantinople, eight emperors ruled in the eastern Roman capital. Their reigns were as successful as they were long. Under John II (1118–43) and Manuel I (1143–80) Byzantium remained a wealthy and expansionist power, maintaining the internal structures and external initiatives which were necessary to sustain a traditional imperial identity in a changing Mediterranean world of crusaders, Turks and Italian merchants. But the minority of Manuel’s son Alexios II (1180–83) exposed the fragility of the regime inaugurated by Alexios I. Lateral branches of the reigning dynasty seized power in a series of violent usurpations that progressively undermined the security of each usurper, inviting foreign intervention, provincial revolts and attempted coups d’état. Under Andronikos I (1183–5), Isaac II (1185–95), Alexios III (1195–1203), Alexios IV (1203–4) and Alexios V (1204), the structural features which had been the strengths of the state in the previous hundred years became liabilities. The empire’s international web of clients and marriage alliances, its reputation for fabulous wealth, the overwhelming concentration of people and resources in Constantinople, the privileged status of the ‘blood-royal’, the cultural self-confidence of the administrative and religious elite: under strong leadership, these factors had come together to make the empire dynamic and great; out of control, they and the reactions they set up combined to make the Fourth Crusade a recipe for disaster.

The Fourth Crusade brought out the worst in the relationship between Byzantium and the west that had been developing in the century since the First Crusade; the violent conquest and sack of Constantinople expressed and deepened old hatreds, and there is clearly some sense in the standard opinion that the event confirmed beyond doubt how incompatible the two cultures had always been.