The five centuries that separate Aristotle’s death in 322 BC from Galen’s ascendancy in Rome in the latter part of the second century AD were fertile ones for the biological sciences, in particular medicine. Nor is the period solely of interest to historians of science-for the methodological debates characteristic of the life sciences of the time shadow, and in some cases foreshadow, those which raged between the contemporary Sceptical and Dogmatic schools. If our knowledge of the medicine of the period is necessarily circumscribed by the fragmentary nature of almost all of our sources, and if the project of reconstructing the science is consequently all the more difficult, the enterprise is none the less a rich, fascinating, and exciting one.