A recent approach of Vegetius’s Epitoma rei militaris — to which the integrality of this study is devoted — tries “to restore to favour” its author, but, in the same time, brings discredit on the work as a source of knowledge for the late Roman art of war, and thus creates an useless tension between the historical and the prescriptive aspects of the text. The author rather thinks that the Epitoma is a well-ordered collection of practices, meant to be applicable. The opposition, placed at the heart of the matter, between the limited and perhaps purely empirical knowledge of the Emperor and his advisers on the one hand, the supposed universal aptitude of the compiler on the other hand, finds a way to be solved by the rewording of multiple and polygenetic experiments, using the literary criteria of the artes militares. It is thus its capacity to write a clear synthesis that Vegetius seeks to promote, maintaining however a clear distinction between the literary models, the only way for the expression of a recognized knowledge, and the applicable standards. Two methodological precautions should make it possible to restore to the Epitoma all its significance. First, a constant attention to the global organization of the text. For instance, it seems obvious that the point of view changes radically between book II and III, which is the compendium of an applicable military knowledge, written for a commander. Second, a precise comparison between the text of the Epitoma and the whole of the literary, documentary and archaeological sources on the late Roman army, which would reveal the relevance of the information contained in the work and show the descriptive value of many chapters, in particular II, 7 or III, 14-20. The question would not be any more to know if the Epitoma could have been used as a manual for Roman officers, but to patiently determine if the standards exposed in it have chances to reflect a contemporary military reality. The present study has precisely as an aim to show the relevance of such a method and its interest for the knowledge of the practices of the late Roman infantry in some tactical and operational fields: intelligence and the preparation for battle, its various phases and its mechanism, the measures to be taken after a victory or a defeat. It is not an exhaustive study of the Epitoma rei militaris, and fields where this work could be taken at fault of confusion (the antiqua ordinatio legionis…), or of lack of originality, were deliberately left out. However, the multiple echoes that the Epitoma awake in the contemporary narrative sources and in the later technical literature show all its relevance as a source for the late Roman military history. Far from being a nostalgic compilation or a whimsical proposal, the Epitoma represents rather, with an historiographic and practical scope, a true ordered compendium of the Roman military tradition, but also of the art of war at the end of the 4th c. AD.