Epidemiology. It is hard to give a precise epidemiology of the ancient Greek world—that is, a clear picture of the kinds of diseases and ailments that were common in the Mediterranean at that time. The preservation of a large body of fifth- and fourth-century Greek medical writings provides less help than might be expected because the categories used by ancient doctors to diagnose their patients were often completely different from modern ones. Many of the symptoms and signs they considered important for identifying diseases are simply irrelevant in modern systems of classification. The same is true of their methods of investigation—the pulse, for instance, was not used as a diagnostic tool until the third century B.C.E.—which often omit what modern doctors consider to be crucial information. Greek physicians neither envisioned nor discussed diseases...