Servetus, an anatomist, astrologer, physician and polymath was an early proponent of the pulmonary circulation of the blood. In 1553, Servetus was burned at the stake in Geneva. Servetus was executed on account of his theological beliefs, particularly his denial of the Trinity and of the deity of Christ in this work. This is an undated manuscript written in two hands. Servetus’ death underscores the potential hazards facing natural philosophers who wrote about theological topics in Protestant realms.