Galen

Galen conducted extensive anatomical studies, primarily on animals such as pigs and Barbary macaques, and developed theories about blood circulation, nerve function, and respiration that dominated Western medicine for over 1,400 years. His systematic approach to physiology and his enormous body of written work made him the single most influential physician of antiquity.

Roman law and cultural taboos prohibited the dissection of human bodies during Galen's time, so he relied on animal dissections and the writings of earlier Greek physicians like Herophilus. This led to significant errors in his descriptions of human anatomy, such as his account of the liver's blood vessels, which persisted until the Renaissance.

Galen's theories remained the unquestioned foundation of European and Islamic medicine until the 16th century, when Andreas Vesalius published 'De humani corporis fabrica' in 1543. Vesalius used direct human dissection to demonstrate that many of Galen's anatomical descriptions were based on animals and were incorrect for humans.

Galen served as a physician to gladiators in Pergamon, in what is now Turkey, early in his career, where he gained extensive practical experience treating wounds. He later moved to Rome and became personal physician to the emperors Marcus Aurelius, Lucius Verus, and Commodus during the 2nd century CE.