Polybius............................

 In London, meanwhile, John Adams composed his best-known work, A Defense of the Constitutions of Government of the United States of America, the sole piece of writing he finished that is longer than an essay. . . .

     In this rambling constitutional study, Adams surveyed all sorts of governments in the ancient and modern worlds, and concluded, as others did, that the most effective and sustainable form is one that is "a mixture of monarchy, aristocracy, and democracy, extolled by Polybius."  That ancient Greek historian had tired in his work to explain the rapid rise of the Roman Republic.  Polybius wrote that he intended to analyze how "it came about that nearly the whole world fell under the power of Rome in somewhat less than fifty-three years."

-Thomas E. Ricks, First Principles: What America's Founders Learned from the Greeks and Romans and How That Shaped Our Country