By his own boast, witch trial judge Pierre de Lancre tortured and burned more than 600 men and women accused of consorting with demons. In his books Tableau de l'Inconstance des mauvais Anges (1613) and L'Incredulite et Mescreance du Sortilege (1622), de Lancre defended the belief in demons, black magic, and witchcraft. In his considered opinion, even to deny the possibility of witchcraft was heresy, for God himself in the Holy Bible had condemned magicians and sorcerers. De Lancre, however, was not a member of the clergy, and his concerns were social, rather than theological. He believed that sorcerers and witches were a well-organized anti-social force that sought to overthrow the established order.
It was customary for the judges of the witchcraft trials to denounce Jews as heretics and sorcerers. De Lancre was no exception, once stating that God had withdrawn his grace and promises from the Jewish people. He claimed also to have it on great authority that many Jews were powerful magicians who had the ability to shapeshift into wolves by night.
De Lancre, as so many of the trial judges, became rather fixated on the details that the witches provided of their carnal encounters with demons. The more questions he asked about these sexual matters and the more torture the witches suffered, the more lurid the accounts became. De Lancre decided that Incubi and Succubi, those demonic seducers of men and women, had as their mission the infliction of a double injury to their victims, attacking them in both their body and their soul.
When men or women accused of being sorcerers protested that the devil had not picked them up and flown them anywhere, Judge de Lancre decreed that those sorcerers who walked to the Sabbats held in the forests were just as guilty as those who were carried to such sites by Satan. De Lancre warned his fellow members of the tribunals to be wary of toads, for they could likely be familiars of the witches. One witch whom he tried and who confessed at length, described a number of toads that had attended a Sabbat in the Basses-Pyrenees region dressed in black and scarlet velvet with little bells attached to their coats and trousers.
In 1609, the Parliament of Bordeaux sent de Lancre to Labourd in the Bayonne district to administer punishment to the sorcerers who had infested the region. In short order, de Lancre deduced that Satan deceived a number of Roman Catholic priests into administering Black Masses to the witches in the area. Two priests, an elderly man of 70 and a young man of 27, were executed almost immediately upon de Lancre's arrival. The horrified bishop of Bayonne arranged for his five clergy members accused of sorcery to escape prison. He also interfered with the judge's orders of imprisonment for three other priests and arranged for them to escape and flee the countryside.
When he was not sentencing men and women to their horrible deaths, de Lancre was known to his Christian contemporaries as a sensitive and talented writer of idyllic pastoral accounts of country living. When he at last retired to his country estate, he turned all of his attention to writing and the construction of chapels, fountains, and grottos to beautify his lavish grounds.