fl. 1200s

French scholar noted for his observations on the magnetic compass and for his work as a military engineer. In 1269 Petrus, also known as Pierre Pelerin de Maricourt, was involved in a siege by the French army against the city of Lucera in southern Italy. While occupied on projects such as making machines for slinging stones and fire-balls against the city, he began to consider the concept of a perpetual-motion machine. In Petrus's conception, a wheel could be kept constantly in motion by use of a magnet. He explained this idea in Epistola de magnete, a letter on the subject written to a layman.