This paper investigates the influence of late Roman military law on the Lex Baiuvariorum – a text, which served as the basis for the Merovingian kings’ organization of the Frankish kingdom’s eastern border-region as a ducatus or duchy. Particular considerations concerning the historical background of the Bavarian duchy’s formation will be addressed, after which provisions for the protection of the Bavarian dux or duke, largely as relates to treason and military discipline, will be investigated. By comparing sources for the Roman crimen laesae maiestatis and other legal texts of Roman military writers, it will be demonstrated that the provisions of the Bavarian law-code clearly bear the influence of Roman military law.