The absence of a professional police force in the city of Rome in classical times is often identified as a major cause of the collapse of the Republic. But this alleged "structural weakness" was not removed by the Emperor Augustus and his successors, and was in fact shared with other premodern states. In this critical new study of the system of law and order in ancient Rome in both the republican and imperial periods, Wilfried Nippel identifies the mechanisms of self-regulation that operated as a stabilizing force within Roman society.