What would count as evidence that thinking belongs in the brain? Galen approached that question through anatomy and argument. His answer also left important roles for the heart and liver. Understanding those roles helps us read his work on its own terms, without turning him into a modern neuroscientist.
A physician in the Roman world
Galen was born in 129 CE in Pergamon, in present-day Turkey, to an architect. He studied medicine and philosophy, became physician to gladiators in 157, and later worked at the imperial court under Marcus Aurelius and his successors. His death is conventionally dated around 200, although later sources suggest he lived longer (P. N. Singer, §§1, 3.1). The exact date is Unknown.
In his account of the soul, rational activity belonged in the brain, spirited responses in the heart, and appetite in the liver. Animal experiments contributed to his arguments about perception and voluntary movement. This is Documented as Galen’s position; saying he proved that the brain alone controls everything would change it into a different claim (Singer, §3.1).
What observation could—and could not—show
His surviving On the Natural Faculties lets us follow an argument rather than just read a list of discoveries. At its opening, Galen distinguishes sensation and voluntary movement from growth and nutrition. His subject includes the different powers he believes belong to different parts of a living body (Arthur John Brock translation, Book I, §§1–4).
Later, he argues that arteries contain blood. But the account also proposes passages through the wall between the heart’s ventricles. He acknowledges that their far ends cannot actually be seen. His reasoning draws on the belief that nature makes nothing without a purpose (Brock translation, Book III, §§14–15).
That passage matters because it shows where seeing ends and inference begins. Documented means we can identify his argument in the text. It does not mean every structure he proposed was demonstrated. A reader can ask two separate questions: What did the writer observe, and what did he conclude from it?
Animal anatomy and the limits of the record
Galen’s anatomical work included animal dissection and experiments. Singer describes his demonstrations involving the spinal cord and a live pig, and explains how these contributed to his argument for the brain’s leading role (§1). These were invasive procedures; no instructions are reproduced here.
His reliance on animals is sometimes explained by a definite Roman legal ban on human dissection. That legal claim is Unknown here. The available evidence supports describing his animal work, without asserting a law that has not been established.
Fluids and qualities
Galen also worked with humoral explanations. The four humors were blood, phlegm, yellow bile and black bile. As discussed in this series’ Hippocrates profile, their clear formulation appears in The Nature of Man, attributed to Polybus. Historian Jacques Jouanna describes how Galen promoted that account while crediting Hippocrates (Jouanna, pp. 320–321, 335–336).
Galen’s Natural Faculties also discusses warmth, coldness, moisture and dryness as basic qualities (Brock translation, Book I, §6). These are Documented historical explanations. They help explain the questions he asked; this page does not turn them into instructions for care or credit him with inventing every earlier balance theory.
Translation involved several hands
Galen’s writings reached new readers through work by several translators. The National Library of Medicine’s catalogue describes the route taken by On the Usefulness of the Parts. Hunayn ibn Ishaq prepared a Syriac version. His nephew Hubaysh translated that version into Arabic, and Hunayn then revised the Arabic translation (NLM, MS A 30.1).
This is Strongly supported by the scholarly catalogue, rather than a claim that the original Syriac copy survives. The catalogue identifies that version as lost. The named sequence preserves something a broad story of transmission can miss: preparing, translating and revising were distinct tasks, performed by identifiable people.
Vesalius both used and questioned Galen
Andreas Vesalius published On the Fabric of the Human Body in 1543. The National Library of Medicine describes his close reliance on Galen alongside dissections that confirmed some claims and challenged others (NLM’s account of its historical anatomy collection).
Both dependence and criticism belong in the story. A later writer could value Galen while disagreeing with him. The publication date is Documented; it is not a date on which every reader suddenly abandoned Galen.
How we know
What survives. Galen’s writings, manuscript catalogues and later anatomical books.
Whose voices are missing. These sources chiefly present learned writers’ arguments, not patients’ own accounts.
What remains uncertain. His death date, the claimed legal ban and how particular readers used his works.
Then vs. now
Then: Anatomy, theories of the soul and arguments about nature appeared together.
Now: We can examine each argument and its evidence without making Galen either an infallible authority or a collection of mistakes.