 While the founders of the city of Rome were said to be the legendary twins Romulus and Remus, Romans would come to identify the origins of their distinctive liberty in the killing of a tyrannical king, generally dated in 509 BCE, by the ancestor of the Junius Brutus who would eventually kill Julius Caesar. The position of king was replaced by two annually elected consuls, the royal council became the Senate, and popular assemblies were established to elect magistrates and pass the laws they proposed. By Cicero’s time, this regime—self-identified as the S.P.Q.R., the “Senatus populusque Romanus” or “Senate and people of  Rome”[13]–  had become interpreted as a version of the “mixed constitution” which had had a long if complicated and until then relatively minor history as an idea in the works of Thucydides, Plato, and Aristotle (Hahm 2009). An influential account of Rome as such a mixed constitution, in this case combining the three classical regime forms of monarchy, aristocracy, and democracy, had already been given by the Greek historian Polybius, who referred to the distinction between the characteristic powers in each kind of regime and their mutual checking and balancing (Histories 6.11–18; see von Fritz 1954). Whereas in Polybius the achievement of balance between the different powers was portrayed as resulting from mutual rivalrous self-assertion, Cicero would refer to it in more harmonious language, a form of balancing (compensatio, De rep. II. 57) with the ideas of mixing and tempering paramount, as observed by E.M. Atkins (2000: 491). (For a useful overview of Roman political thought, see J.W. Atkins 2018.)