The protagonist of this book is a Roman political theory which helped to define the intellectual and ideological contours of the European early-modern state by performing an important historical and conceptual role in the formation of the Renaissance prince. This role has gradually become obscured over recent centuries, and the main purpose of the following chapters is to try to illuminate it. My explanation of the theory's contribution to the history of the sovereign state consists in two basic parts. The first is in terms of its conceptual character: it is a theory about the sovereign princeps, and an argument which is explicitly concerned to delineate a series of relations between the princeps and the status of various entities. So, for example, the prince is said to have the ‘state’ of those persons whom he governs in his hand; he is described as a tutor of ‘the public state’ and his principatus is supposed to reflect the ‘state of the world’. These claims are connected to a distinctive way of thinking about persons which considers their status from the point of view of the universal law of reason, rather than from a purely local legal perspective. The theory holds that persons should be governed according to the same rationality which governs the cosmos. One consequence of this approach was that it introduced to Roman political discourse a novel way of looking at the question of what a free or unfree person was.