See also: Castelnau

Pierre de Castelnau was born in? and dead the January 15th 1208 close to the abbey of Saint-Gilles-of-Gard.

Monk of Cîteaux and archdeacon of Maguelone, Cistercien French, it vainly tried to dam up the Hérésie Cathare in the South of France, with the extraordinary quality of Légat of the pope Innocent III, to seek the heretics Albigensian and to deliver them to the secular arm, and had as a colleague Ramier, monk of Cîteaux. They were accompanied inter alia Dominique de Guzmán, founder of the Ordre of the Preaching friars. These Inquisiteur S met a sharp resistance, and Castelnau ends up being assassinated in Trinquetailles, near Arles on the grounds of Raymond VI, count de Toulouse (1208), at the moment when it had just enjoined this prince to give up the cause of the Albigensians. The murderer was a rider of Raymond VI, who, suspecté, was excommunicated. This event is at the origin of the Albigensian Crusade.

Declared martyr by Innocent IV, then béatifié, it is celebrated on January 15th in the dioceses of Carcassonne and Nimes.