Practical interest in astrology, alchemy, and other departments of the occultist tradition ran strong throughout the early modern period among serious thinkers in many disciplines. Franco Burgersdijck, Tommaso Campanella, and Robert Fludd showed their century three ways to befriend occultism. Like Burgersdijck and other school philosophers, one could propagate the traditional Aristotelianism that sustained belief in magic. One could replace the Peripatetic basis of magic with a new system intended to be intelligible as philosophy, which was Campanella's aim. Like Fludd, one could detach occultism both from philosophy's Aristotelian past and from its Cartesian future. Marin Mersenne launched his crusade against occultism sometime before 1620, when he began to assemble his huge Genesis commentary of 1623. Mersenne aimed his book at atheists and deists, and among the subverters of religion he counted Fludd and many others who argued for magic.