This book is not a biography of the Emperor Julian, nor a history of the late antique Roman army. Rather, its goal is to study the dynamic of the battles in which Julian was the protagonist during the brief span of his public life, which lasted only a little more than seven and a half years (355-363). The public life of the young emperor was, in fact, a continuous succession of battles. By examining Julian's military campaign, we may retrace the organizational and military structure of the late antique Roman empire.