In his study, Charles Oman examines the development of military art in the Middle Ages - from the period of the fall of the Roman Empire to the beginning of the 16th century. Analyzing the evolution of methods of warfare, the author examines the conditions in which the foundations of military art were born, the political situation preceding military operations, gives characteristics of the organization of the armies of different European countries, notes the features of their weapons. The author supports his own observations and conclusions with excerpts from the works of famous commanders. The book contains a plan illustrating the main features of the Byzantine tactical system, and provides diagrams that allow one to imagine the disposition of enemy forces in the famous battles: Granson, Murten, Agincourt, Bannockburn, Crecy and Poitiers.