The author is a specialist in military history and the author of eleven books and nearly 200 articles. His main subject of study is the late Roman army and the warriors of the early Middle Ages, but he also places himself in the broader perspective of comparative military history. A graduate of the regional sessions of the Hautes Etudes de l'Armement and of the Institut des Hautes Etudes de la Defense nationale (France), he has also been a member of the Scientific Committee of the Centre d'Histoire et de Prospective Militaires de Lausanne-Pully (Switzerland) and research director at the Institut fur vergleichende Tactik in Vienna-Postdam (Austria-Germany). He regularly writes for the Revue Militaire Suisse for nearly three decades, and for three years has directed dissertations at the Ecole de Guerre (Paris).