Galen was a prominent physician whose work formed the basis of medical theory and public health in the Medieval era.

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Galen Galen

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Table of contents

    This article will look at Galen's life and notable works before examining his medical discoveries and his development of humoral theory. Finally, we will look at the impact of Galen's work in the Medieval world.

    So, who was Galen? Why was he so important in the history of medicine, and how did his work influence public health in medieval Britain?

    Galen Biography

    Claudius Galen was born in Pergamum (modern-day Turkey) to Greek parents in around 130 AD. His family was wealthy, and he had a good education. In approximately 160 AD, he moved to Rome and remained there for the rest of his life.

    He pioneered new forms of medical theory and practice, was a prolific writer and was very well respected. He became the personal physician of Emperor Marcus Aurelius and his successors Commodus and Septimius Severus.

    Galen Drawing of Galen StudySmarterFig. 1 - An 18th-century portrait of Galen

    His work would form the basis of European medical knowledge for the next 1,500 years, having been preserved by Arab scholars after the fall of the Roman Empire. It wasn't until the Renaissance that his theories began to be challenged and discarded.

    The Works of Galen

    Galen was a prolific writer, using secretaries to dictate his works. Unfortunately, many of Galen's works were lost - partly through being lost over time, but also after a large fire that destroyed a warehouse where Galen stored his works. Nevertheless, the surviving works measure nearly 20,000 pages and account for 10% of all Ancient Greek literature written before 350 AD.

    Some of his most notable works include:

    • On the Natural Faculties.
    • The Art of Medicine.
    • The Method of Medicine.
    • On Good Bodily State.
    • On the Constitution of the Art of Medicine.
    • The Soul's Traits Depend on Bodily Temperament.

    Although he was a physician, much of his work was written in a philosophical tone. This is because Galen believed that medicine was philosophy in action.

    The Invention of Galen

    One of Galen's most significant creations was the development of the experimental method of medical investigation. He was a great advocate of dissection for research purposes and to improve surgical skills. He believed that a good knowledge of anatomy was key to understanding and developing medicine.

    Did you know? Galen's keen observation of animal dissections allowed him to distinguish many facts about how a body worked. For example, he correctly observed that urine was produced in the kidneys and noted the differences between arteries and veins.

    One of his most important discoveries was that arteries were filled with blood, not air. This had been an accepted fact for the previous 400 years.

    Galen Diagram of Galen's anatomy StudySmarterFig. 2 - An interpretation of how Galen viewed the workings of the human body

    However, Galen's work was limited. Firstly, he could only dissect animals - to dissect a human body was unacceptable in Roman society. Secondly, because of this, his drawings of human anatomy were often wrong - since he had to infer human anatomy from an animal's anatomy, he often made errors.

    Galen Theory

    The part of Galen's work that is most relevant to Medieval Britain is his development of the Theory of the Four Humours, a.k.a. Humoral Theory.

    Humoral Theory had first been put forward by the Ancient Greek physician Hippocrates. Essentially, he had theorised that the human body contained four humours that controlled a person's personality and could affect their health.

    The four humours were:

    • Blood
    • Phlegm
    • Yellow Bile
    • Black Bile

    The diagram below shows how the properties of the four humours were understood.

    Galen Humoural Theory StudySmarterFig. 3 - A diagram showing the four humours and what they were associated with

    Galen based a lot of his work on that of Hippocrates. He agreed with Hippocrates' ideas that the body should be treated as one system rather than just a collection of parts. Equally, he advocated for Hippocrates' method of medical observation to help diagnose illnesses.

    Galen also developed a system of remedies based on humoral theory. If an imbalance of the humours caused illness, then the remedy must be to rebalance them.

    How did Remedies based on Humoral Theory work?

    Galen might diagnose a patient as having too much Phlegm, which is causing their illness.

    According to humoral theory, Phlegm is cold and wet. Therefore, Galen needs to give the patient the opposite of that to rebalance their humours and heal them.

    If Phlegm is cold and wet, Galen would prescribe something hot and dry.

    This might be a poultice of something like mustard seed. If a person was wealthy, he might tell them to wear a gold amulet - gold was associated with the hot and fiery sun.

    Impact in the Medieval Era

    Galen's works were preserved well after he died in c. 210 AD. They became the basis for European medicine until the Renaissance.

    Galen and the Church

    The Church was the chief authority on medical matters in Medieval Britain. They copied and published nearly all books and written works until the invention of the printing press in the 1400s.

    They spread the works of Galen to training physicians because his work was trusted, having been the cornerstone of medicine for so long. In addition, Galen's work had been studied by theologians and was seen to be common knowledge.

    Did you know? Galen also believed in the soul and that it had been created by a higher being. As this was the foundation upon which his medical theories were built, it was more acceptable to the Church.

    Galen Contribution to Medicine

    Humoral theory was the foundation of medical theory in the Medieval era. It influenced the remedies that physicians would prescribe and the mixtures that apothecaries would sell.

    Here are some popular remedies based on humoral theory that were commonplace during the Medieval era:

    • Phlebotomy (Bleeding): This involved cutting the skin or using leeches to drain some blood from the body to rebalance the humours.

    • Purging: This was a remedy used when doctors diagnosed a person with too much yellow bile. It was believed that food was used to create the humours, so to rebalance the humours, you had to get rid of the food. This would be done using an emetic, forcing someone to vomit, or a clyster, which would make them go to the toilet.

    • Theriac: A mixture of spices, herbs and other ingredients that were thought to cure minor illnesses. This remedy was popular, as Galen himself had written about it.

    After the Medieval period, Galen's theories, like the four humours and remedies like bleeding and purging, were used less as newer ideas about medicine took precedence over them. However, some of Galen's methods, like dissection and clinical observation, remained central principles of medicine and medical learning.

    Galen's work was eventually criticised in the Early Modern period (16th-18th centuries). Andreas Vesalius, a Belgian physicist and anatomist, criticised and challenged lots of Galen's theories about how the body worked. Yet, the Church and society were unwilling to let go of Galen's ideas, and Vesalius' criticism was not well received. It would be a long time before Galen's theories stopped being accepted as medical fact.

    Did you know? Humoral theory, one of Galen's key ideas, was still believed in by the public until the 1800s! The trust and belief in Galen's work did not disappear easily, especially for ordinary people - it was treated as common knowledge and passed down from generation to generation.

    Galen and Public Health

    Since Galen's theories were considered common knowledge, they also affected public health, especially in treating epidemic diseases.

    The Black Death

    Galen's theories were employed when the Black Death swept through Europe in 1347 to try and cure the disease. In particular, bleeding was used as a cure to rebalance the humours. In reality, blood loss only weakened the patient and and made them less able to fight off the disease!

    Galen's theories did not provide much aid in curing diseases which were big public health issues in the medieval period; as the root theories were incorrect, the treatments were also ineffective because they were not targeting the disease correctly. In many cases, methods like bleeding and purging only made the patient's immune system less able to heal the body because it was being drained of blood and nutrients.

    Galen Theriac preparation painting StudySmarterFig. 4 - The preparation of a Theriac from the Tacunium Sanitatis, a medieval medical text

    Galen and his Contributions to Medicine - Key takeaways

    • Galen was a Roman physician who lived from 130 AD to 210 AD. He was born in Pergamum to Greek parents and was well-educated.
    • He moved to Rome and became a respected doctor and was the personal physician of three Roman emperors.
    • He developed medical experimentation to learn about anatomy and dissected animals to learn how bodily systems worked. From this came many important medical discoveries.
    • He developed humoral theory, which Hippocrates had invented.
    • His work was preserved after the fall of Rome and became the cornerstone of medicine in the Medieval era. His work was trusted by the Church and disseminated to training physicians.
    • It was the basis for many common diagnoses and remedies in Medieval public health.


    1. Fig. 2 Galen's "Physiological system" ( by Wellcome Images ( licensed under CC BY 4.0 (
    Frequently Asked Questions about Galen

    Who is Galen?

    Galen was a physician born in Pergamum (modern-day Turkey) in 130 AD who operated within Ancient Rome. He was the personal physician of some Roman Emperors (Marcus Aurelius, Commodus and Septimus Severus) and developed key medical theories that influenced the understanding of public health for around 1,500 years!

    What was Galen's main discovery?

    Galen had many theories and discoveries - one of the most important was that arteries were filled with blood, not air, which had been believed for 400 years until his work. He also developed and advocated Hippocrates' Theory of the Four Humours.

    What was Galen's theory of opposites?

    Using Humoral theory, Galen believed that if a patient had too much phlegm (considered cold and wet) the remedy would be something hot and drying, such as a poultice of mustard seed or wearing something gold (as gold was associated with the hot and fiery sun). The theory of opposites was therefore using the opposing characteristics of symptoms to cure an illness.

    What were Galen's ideas?

    Galen published many works on medical theory. His key ideas revolved around Hippocrates' Theory of the Four Humours, whereby the body contains four humours and they were responsible for illness and personality. An unbalanced humour would result in illness.

    What was Galen's contribution to medicine?

    A key contribution to medicine by Galen was that arteries were filled with blood, not air. He used animal dissections to determine facts about the human body, such as that urine was produced in the kidneys and the difference between arteries and veins.

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