Michael Servetus is arrested by John Calvin in Geneva, Switzerland as a heretic.

Michael Servetus (1511–1553) was a Spanish theologian, physician, and polymath whose radical religious views placed him at odds with both Catholic and Protestant authorities during the turbulent years of the Reformation. Born in Villanueva de Sigena, Aragón, Servetus was highly educated, studying law, medicine, and theology across Europe. He is best remembered for his rejection of the orthodox Christian doctrine of the Trinity, which he saw as a corruption of the original biblical message. In his 1531 work De Trinitatis Erroribus (On the Errors of the Trinity), Servetus argued for a unitarian conception of God, claiming that the Father, Son, and Holy Spirit were not distinct persons but manifestations of one divine being. His unorthodox theology, paired with his attacks on infant baptism, drew sharp condemnation from both Roman Catholic authorities and leading Protestant reformers.

Servetus was not merely a theological dissenter—he was also an accomplished scientist and physician. While practicing medicine in France, he published influential works on pharmacology and was among the earliest European thinkers to describe the pulmonary circulation of blood, anticipating William Harvey’s later findings. Yet his intellectual versatility did not shield him from persecution. Servetus’s ideas became known to John Calvin through their extensive correspondence, in which Servetus openly challenged Calvin’s theology. When he published Christianismi Restitutio (The Restoration of Christianity) in 1553, he doubled down on his rejection of Trinitarianism and predestination, directly opposing Calvinist doctrine. This sealed his fate: the book was immediately banned, and Catholic authorities in France condemned him for heresy.

Attempting to flee to Italy, Servetus passed through Geneva, where he was recognized and arrested under Calvin’s influence. His trial in Geneva was swift and uncompromising. Despite opportunities to recant, Servetus refused to renounce his beliefs, maintaining that he was defending the truth of Scripture. Found guilty of heresy and blasphemy, he was sentenced to death by burning at the stake—a fate carried out on October 27, 1553, with a copy of his Christianismi Restitutio tied to his side. His execution became one of the most infamous episodes of the Reformation, sparking debates over religious tolerance and the right to dissent. To this day, Servetus is remembered as both a brilliant Renaissance thinker and a martyr for intellectual and theological freedom.