One one looks at Polybius’s treatment of revolutions in Book 8 of his History, it looks as if he never read Aristotle’s Politics book 5.  In fact Polybius’s account of the cycle of politeia looks more indebted to Plato and to Plutarch than to Aristotle.  What evidence is that Polybius knew of Aristotle’s Politics, or like most Roman authors, Aristotle’s Politics was unknown to him?