In the Imperial books of his Roman History, Cassius Dio focuses on individual emperors and imperial institutions to promote a political framework for the ideal monarchy, and to theorise autocracy’s typical problems and their solutions. The distinctive narrative structure of Dio’s work creates a unique sense of the past and allows us to see Roman history through a specific lens: that of a man who witnessed the Principate from the Antonines to the Severans. When Dio was writing, the Principate was a full-fledged historical fact, having experienced more than two hundred years of history, good and bad emperors, and three major civil wars. This collection of seven essays sets out to address these issues, and to see Dio not as an ‘adherent’ to or ‘advocate’ of monarchy, but rather as a theorist of its development and execution.