Treatise On TolerationOne of the most important essays on religious tolerance and freedom of thought In 1762 Jean Calas, a merchant from Toulouse, was executed after being falsely accused of killing his son. As it became clear that Calas was in fact persecuted for being a Protestant, Voltaire began a campaign to get his sentence overturned and in the process made the case for some of the most important values upheld by the Enlightenment, from religious tolerance to freedom