Galen

Galen was born around 129 CE at Pergamon, in what is now western Turkey, a city famous across the Greek world for its sanctuary of Asclepius, the healing god, to which the sick traveled to sleep in a sacred precinct and receive diagnostic or therapeutic dreams. Galen himself recorded that his father, an architect, changed his intended career from philosophy to medicine after a dream instructed him to do so, and Galen credited dreams sent by Asclepius at several further points in his own medical training, treating the god's guidance as continuous with, rather than opposed to, his rigorous anatomical and clinical study.

He trained at the Pergamon Asclepeion itself and served there as physician to the city's gladiators, a post that gave him direct experience of traumatic wound anatomy no textbook study could match, before travels to Smyrna, Corinth and Alexandria completed his education. He settled in Rome around 162 CE, where his skill and confidence secured him the position of physician to a succession of emperors, Marcus Aurelius, Commodus and Septimius Severus among them, and where he produced the overwhelming bulk of the immense body of writing, on anatomy, physiology, diagnosis, pharmacology and philosophy, that made his name the single most authoritative one in medicine for the next fourteen centuries.

Galen inherited from the Hippocratic corpus the theory that health depends on the balance of four bodily humors, blood, phlegm, yellow bile and black bile, and he extended it into a full theory of temperament, arguing that the relative dominance of each humor in an individual produces a corresponding disposition, sanguine, phlegmatic, choleric or melancholic, that shapes not only susceptibility to disease but personality itself. This fusion of physiology and character reading gave Western medicine a working model of the person that lasted, essentially unchallenged, into the early modern period, and it fed directly into later systems, astrology among them, that mapped the four humors onto the four elements and the planets, treating bodily constitution and psychological type as two readings of the same underlying pattern.

Galen's medical corpus, running to hundreds of individual treatises, was translated into Syriac and Arabic within a few centuries of his death and became the backbone of medieval Islamic medicine under physicians such as al-Razi and Avicenna, who both extended and occasionally challenged him, before Latin translations carried the same authority into medieval and Renaissance European universities. Only with the sixteenth century anatomical work of Andreas Vesalius, which corrected numerous errors traceable to Galen's having dissected animals rather than human cadavers, did his authority in anatomy specifically begin to be displaced, though his broader humoral framework persisted in popular use well beyond that.