I offer a new account of Polybius’s famous cycle of regimes and why it still matters for constitutional theory. Beyond a familiar classical model of the death of democracy (in which demagogues call for redistribution, leading to elite backlash and a turn to a strongman), I show how Polybius diagnoses a deeper danger: cheirokratia, a reign of violence in which citizens lose faith in the possibility of shared norms governing political life. I argue that the cycle’s “return to monarchy” is best understood not as naturalistic historical repetition but as the collapse of politics as a shared normative enterprise. I link my analysis of Polybian cheirokratia to Greek constitutional thought more broadly and to later historians of Rome analyzing moments of constitutional breakdown.