The form of medicine that arose in fifth-century Greece, associated with the name of Hippocrates and later popularized by Galen, marked a major innovation in the treatment of disease. Unlike supernatural theories of disease, Hippocrates' method involved seeking the causes of illness in natural factors. This method rested upon an analogy between the order of the universe and the composition of the body’s "humors." Health, on this view, was a matter of achieving equilibrium between competing humoral forces. Although Hippocratic theory would later be challenged for a number of different reasons, notably including the experience of epidemic diseases, it persists today in various traditions of holistic medicine.