Ancient Roots. As in the rest of science, the medieval world inherited its theories of health from the ancients and based its attempts at remedies on a simplistic and idealized understanding of how the human body works. The most important source of medical knowledge came from a Greek doctor named Galen, who was the personal physician to Emperor Marcus Aurelius in the first century C.E. Galen wrote hundreds of works, and at least 120 of his works on medicine survived to the Middle Ages. Some of his works were available in Latin as early as the fifth century and continued to be translated from the Greek or from Arabic translations from the tenth to the fifteenth centuries. Galen's most important contributions to medieval medicine were the theories of the humors and pneuma (spirit). The idea of humors apparently originated in the...