According to Polybius, the kyklos, or political cycle, rotates through three forms of government — democracy, aristocracy, and monarchy — and the degenerate forms of each of those three — 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 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.