 He lived for a long time in Mons in Hainaut in the Netherlands.At the beginning of his career, he was in the service of Peter of Luxembourg, Count of Saint-Pol, and then he acted in the Naples court of Alfonso V of Aragon.In his work "Le Blason des Couleurs en armes, livrées, & devises" (1414), Courtois developed a heraldic system consisting of the tinctures, planets and carbuncles, the virtues, metals, months, the zodiac, and weekdays among others.