Who Galen was
Galen was a Greek physician and writer born in Pergamon, in what is now western Turkey, in about 129 CE. He died some time around the turn of the third century, though the exact date is uncertain. His father was an architect who supported his education, and Galen studied philosophy and medicine in several centres, including Pergamon, Smyrna and Alexandria. He is known above all for the large body of his writings that survives, which makes him one of the best-documented figures of ancient medicine.
His home city already had a reputation for learning, including its Pergamon library, and it also contained a sanctuary of Asclepius. Galen later said he owed his choice of medicine partly to a dream, which tells us how naturally the religious and the scientific lived together in his world.
From gladiators to the emperor’s household
Early in his career Galen served as physician to the gladiators at Pergamon, whose gladiatorial games produced a steady flow of severe wounds and gave him unusual experience in treating them. He later moved to Rome, where he gained fame through public demonstrations and through treating prominent patients. He had some connection to the imperial court, including service to the emperor Marcus Aurelius, though the details, such as the length of his stays in Rome and his movements, are drawn largely from his own accounts. He was confident, combative and sometimes boastful, and it is worth reading his own claims with that in mind.
Anatomy without human dissection
By Galen’s time, dissection of human bodies was not normally practised, despite the brief experiments in Alexandria in the third century BCE. Galen therefore relied on three main sources of knowledge. The first was animal dissection, often of pigs, goats, and Barbary apes (macaques), which he chose because they were similar to humans. The second was the observation of injuries, as in the gladiators he treated. The third was occasional access to exposed human bones and to the works of earlier anatomists.
He also performed experiments on live animals. Cutting particular nerves in a pig, for example, showed how the voice was affected, which helped to establish the role of nerves in controlling the body. He demonstrated that arteries carry blood and not air, which was an important correction to some earlier views. Such demonstrations were a major part of his reputation.
Where animal anatomy misled him
Because he dissected animals, he sometimes described structures that humans do not have, or that differ in humans. The standard example is a network of blood vessels at the base of the brain, called the rete mirabile, which is present in some animals but not in people. Galen’s descriptions of the liver, heart and uterus also contain features better matched to animals. These errors are not carelessness so much as a result of the method’s limits.
His physiology was also mistaken in important ways. He held that the liver made blood and that blood was consumed in the body, rather than circulating continuously. The circulation of the blood was only demonstrated much later, in the seventeenth century.
Theory behind the anatomy
Galen’s anatomy was part of a larger system. He accepted the humoral theory inherited from the Hippocratic tradition, in which health depended on the balance of bodily fluids, and he combined it with ideas from Plato and Aristotle about the soul having several parts. He linked these parts to different organs, such as the brain, heart and liver. He believed that nature acts with purpose, so that each organ is designed for a function, and this belief guided his reading of anatomy.
He also wrote about drugs, diet, diagnosis (including taking the pulse), and the training of physicians. He insisted that a good doctor should also be a philosopher, trained in logic and in observation.
A body of writing that survived
Galen wrote on a very large scale. A significant amount of his work survives in Greek, and further works exist only in translations into Arabic and other languages. Some of his works were lost when storage buildings in Rome were damaged by fire, according to his own account. Scholars still attribute some texts to him with caution because ancient authors were sometimes falsely credited.
Why his influence lasted
After his death his writings were studied, summarised and translated, first in the late Roman world and the Byzantine East, later in the Islamic world, where scholars such as the translators working in Abbasid Baghdad rendered many of his books into Arabic, and then in medieval Europe through Latin. His work became part of the standard curriculum for physicians. His clear, systematic approach and his apparent completeness gave his work great authority.
That authority also became a problem. For centuries, if the body did not match Galen’s description, some scholars assumed the body was at fault. In the sixteenth century, Andreas Vesalius published a detailed anatomy based on human dissection, and it corrected many of Galen’s errors. Galen’s reputation was reduced, but he remained historically important as the central link between ancient and later medicine.
A fair assessment
Galen combined real observation and experiment with strong theoretical assumptions. Some of his work, such as the study of nerves and the demonstration that arteries contain blood, was a genuine achievement. Other parts were mistaken because he had no access to human dissection and no way of testing some ideas. Judging him by modern standards would not be fair; judging him as a skilled and influential figure in Greco-Roman medicine is much more informative.