Hippocrates was the Greek physician (460–370 BC) credited with establishing a theory for the practice of medicine that was distinct from philosophy, mysticism, and theurgy, the tradition of using rituals to evoke the gods for healing. Instead he believed that rather than a punishment inflicted by the gods, disease was the product of environmental factors, diet, and living habits, what today we would call lifestyle choices.
Hippocrates theorized that an imbalance of the four bodily humors (blood, black bile, yellow bile, and phlegm) caused disease. His contributions revolutionized the practice of medicine. Moreover, others regarded his theory as too great to be improved upon. Accordingly, no significant advancements were made until Galen (129–216 AD), a physician living in the Roman Empire. But through the magic of art, we can see the physicians together in this 12th century mural in Anagni, Italy.
Galen extended Hippocrates’s theory of humors to account for the various human temperaments. In other words, an excess or deficiency of any of the humors influences not only human health but determines an individual’s temperament. This theory, humorism, was the earliest to link the physical with the mental and emotional and prevailed in Europe as the most comprehensive view of the human body until the nineteenth century.