By going back over the reasons that led the most powerful king of the West to take up the crusade in 1267, at the age of 53, without any clear motive, we will try to understand why this "last crusade " is a clean break in the history of France's relationship with the world; to the point of forging the late and, to say the least, "colonial " myth of a possible conversion of Saint Louis to Islam on his deathbed