How did "revolution" obtain its particular meanings in political thought? This article examines the role played by translations of Polybius's Histories (Book 6), where "revolution" was the near-unanimous choice for rendering "anacyclosis." It further claims "revolution" displaced the earlier Aristotelian vocabulary of political change (in translations, "mutation" and "sedition"). Finally, it argues that recognizing the Polybian source of much "revolutionary" language in the early modern period fills in an important chapter in the conceptual history of revolution. For Polybians, revolution was a problem to be solved by a mixed government. Only in the eighteenth century would revolution become a solution.