Pierre de Castelnau
（重定向自Peter of Castelnau）
![St Gilles - Church, October 2006](/Images/godic/202502/02/West_church_portal_in_St-Gilles-du-Gard4042.jpg")
Pierre de Castelnau (died 15 January 1208), French ecclesiastic, was born in the diocese of Montpellier.
He was archdeacon of Maguelonne, and in 1199 was appointed by Pope Innocent III as one of the legates for the suppression of the Cathar heresy in Languedoc. In 1202, he became a Cistercian monk at the abbey of Fontfroide, Narbonne, and he was confirmed as Apostolic legate and first inquisitor, first in Toulouse, and afterwards at Viviers and Montpellier.