Lawrence Mott's study of the War of Sicilian Vespers provides an unprecedented view of the internal organization and operations of a medieval fleet. While the conflict of 1282-1302 between France and the crown of Aragon for control of Sicily had broad geopolitical implications, it was also notable for having been fought primarily at sea. Mott draws on previously overlooked archival materials, most notably the battle fleet accounts of Roger of Lauria discovered in the Archives of the Cathedral of Valencia, in order to produce an account of unprecedented detail, full of original insights into the mechanics of naval warfare in this early period. Mott provides detailed information about ship construction, manning, naval tactics and strategy, and especially administration, illustrating how the fleet was created, organized, and maintained despite its composition: a polyglot of different groups, including a significant but previously unknown Muslim contingent. He also offers a military biography of the inexplicably obscure naval commander Roger of Lauria, among the great maritime leaders of all time. Challenging assumptions concerning the war and medieval naval warfare in general, Mott demonstrates that it was remarkable fleet organization and leadership, not "luck" as many have claimed, that defeated the French and ultimately removed them as a major player in the Mediterranean for several centuries. Finally, Mott puts the details and statistical and typological information of his account in perspective with an analysis of the nature of sea power and its changing character over time, challenging the assumption by recent scholars that Mahanian doctrine does not apply to medieval naval warfare.