The emperors of the Komnenian dynasty orchestrated the economic and military renewal of the Byzantine Empire. In 1081, Alexios I became emperor of a bankrupt and diminished empire. In 1180, Manuel I ruled the most powerful state in the eastern Mediterranean, capable of sending expeditions to Egypt, Hungary, Italy, and Palestine. This study examines how the Komnenian emperors restored the Byzantine state by building a professional army of mercenaries and Byzantine citizens. It examines the army's ethnic composition, tactics, equipment, and its financial support. Finally, it examines the army in battle. This is the only study of the Byzantine army during the privotal twelfth century. It provides an explanation for the complex Byzantine political and military problems of the eleventh and twelfth centuries, as well as another perspective on the European crusading movement.