The Kyklos (Ancient Greek: κύκλος, IPA: [kýklos], Cycle) is a term used by some classical Greek authors to describe what they saw as the political cycle of governments in a society. It was roughly based on the history of Greek city-states in the same period. The concept of "The Kyklos" is first elaborated in Plato's Republic, chapters VIII and IX. Polybius calls it the anakyklosis or "anacyclosis". (1)

According to Polybius, who has the most fully developed version of the cycle, it rotates through the three basic forms of government, democracy, aristocracy, and monarchy and the three degenerate forms of each of these governments ochlocracy, oligarchy, and tyranny. Originally society is in anarchy but the strongest figure emerges and sets up a monarchy. The monarch's descendants, who because of their family's power lack virtue, become despots and the monarchy degenerates into a tyranny. Because of the excesses of the ruler the tyranny is overthrown by the leading citizens of the state who set up an aristocracy. They too quickly forget about virtue and the state becomes an oligarchy. These oligarchs are overthrown by the people who set up a democracy. Democracy soon becomes corrupt and degenerates into mob rule, beginning the cycle anew.