Friedrich Förner, a principal architect of the Catholic Reformation in Bamberg, is especially remembered for his 1626 treatise on witchcraft, Panoplia Armaturae Dei. An examination of the full range Förner’s writings reveals a common logic that underlay his approach to the problems of witch-hunting and Catholic reform. From a historical perspective, the rise of witchcraft and Calvinism together represented the final stage in the devil’s assault on Christianity. With the defeat of the Calvinist heresy in the first stages of the Thirty Years’ War, in desperation the devil had employed witches in a last-ditch effort to destroy the Catholic faith. Förner’s reconstruction of ecclesiastical history provided the ideological justification for the final assault on witchcraft, culminating in the trials of the 1620s and 1630s.