Historical and literary research by Jacques Marcal is devoted to the mysteries of the Qatari heresy and the secrets of the castle of Montsegur, their last stronghold in the hopeless confrontation between the King of France and the Roman Catholic Church. What in the doctrine of the Cathars endowed them with such powerful and merciless enemies. What the last initiates hid in an impregnable fortress and managed to endure on the eve of surrender. Whether it was the Holy Grail, or the treasures of the Jerusalem Temple.