The 'principate', the system of government created by Augustus for imperial Rome, has puzzled ancient historians since the days of Theodor Mommsen. Mommsen, whose ancient history classes Max Weber attended, modelled the principate as a political system sui generis, which was, constitutionally, the continuation of the Roman Republic, but in which the ruler was, essentially, an illegitimate military dictator. Instead of applying the doctrines of classical legitimacy, this paper proposes that Weber's three types of legitimate authority better explain the complexities of the Roman Empire from Augustus to the 3rd century ad. While there were numerous elements of 'traditional' and 'legal' authority built into the principate, the individual rulers' legitimacy largely rested on 'charisma'. Individual 'charisma' could become hereditary: whole dynasties relied on 'charismatic' founding fathers, such as the Julio-Claudian (Augustus) and the Flavian (Vespasian) houses. With its intrinsic contradictions and the analytical difficulties it poses, the Roman principate is the ultimate testing ground for Weber's ideal types. [ABSTRACT FROM AUTHOR]