Aegean physician Hippocrates (c. 455–360 B.C.E.) was the first to define the profession of physicians, making up the Hippocratic oath—urging physicians to separate medicine from religion—and is thus considered by some as the “father of medicine.” Some of the first studies of human anatomy were carried out by Roman physician and anatomist Galen (c. 130—200 C.E.). Not only was he the first to use the pulse as a diagnostic aid, but he also wrote all medical knowledge that existed at the time into one systematic treatment—one that would be used by physicians until the end of the Middle Ages.