On this date, 27 October 1553, Michael Servetus, physician and theologian, was burned at the stake in Geneva, Switzerland, for the crime of rejecting the doctrine of the Trinity. He was the first European to describe pulmonary circulation. The description, unnoticed by any of the heretic hunters who examined Servetus’ books, was hidden in the book that Calvin ordered to be burned along with Servetus himself.
A full description of Servetus’ trial and execution can be found in Lawrence and Nancy Goldstone, Out of the Flames: The Remarkable Story of a Fearless Scholar, a Fatal Heresy, and One of the Rarest Books in the World, or Roland H. Bainton, Hunted Heretic: The Life and Death of Michael Servetus, 1511-1553.
Read more here.