Any proper investigation of Machiavelli’s conceptualization of the state has to commence where his own investigation begins: with his definition of what states are. Accordingly, this chapter elucidates the particular theory of definition which informs Machiavelli’s theory of lo stato. Machiavelli is continually preoccupied with what we ‘call’ things – or how we ‘nominate’ them, as he sometimes puts it. These are matters of definition in a technical sense, pursued according to a set of argumentative procedures derived from the pages of the ancient Roman rhetorical theorists Cicero and Quintilian. This chapter reconstructs their theory of definition, showing how they classify things in rhetorical argument, before turning to illustrate the theory in action in Roman antiquity by examining how the concept of the civitas – the crucially important political noun used in classical Latin to denote ‘the city’, ‘city-state’, or ‘citizenry’ – is handled in the writings of Cicero, Seneca, and Augustine. The second section of the chapter analyses the reception of this theory and its application to the idea of the civitas in medieval and Renaissance political culture in order to explain how and why Machiavelli comes to rely upon it.