Robert T. Radford, Cicero: A Study in the Origins of Republican Philosophy. Amsterdam, 2002.

Annotation:

–  This book presents Cicero’s natural law theory, including valuable definitions of the state, the ideal state, the ideal ruler, and the laws for the ideal state. Explanations are offered of the Greek sources of Cicero’s republican philosophy, his influence on the Principate of Augustus, and his role in the development of modern political philosophy.