"Life, liberty and the pursuit of happiness" is perhaps the most famous phrase of all in the American Declaration of Independence. Thomas Jefferson's momentous words are closely related to the French concept of "liberte, egalite, fraternitye"; and both ideas incarnate a notion of freedom as inalienable human right that in the modern world we expect to take for granted. In the ancient world, by contrast, the concepts of freedom and equality had little purchase. Athenians, Spartans and Romans all possessed slaves or helots (unfree bondsmen), and society was unequal at every stratum. Why, then,...