The legend of the seduction of human women by the rebel angels and the sinister character of their offspring, the Nephilim, resonated in the imagination of western authors for centuries. How could spiritual creatures composed of air intermingle with mortals to produce children? From late antiquity onward, Christian writers fused pagan tales about lustful agricultural gods with biblical and apocryphal traditions to fashion stories about seductive demons known as incubi. As Bishop Isidore of Seville (ca. 560–636) explained in his encyclopedic compendium of ancient learning called the Etymologies, incubi took their name from the Latin verb incumbere (“to lie upon”), a nod to their active role during intercourse. Demons also appeared in female form called succubi in order to seduce men. Early medieval authors did not place much stock in the reality of incubi and succubi, but after the turn of the first millennium they appeared more frequently in religious discourse. Preachers crafted moral lessons from rumors about their depredations, while theologians attributed the rise of witchcraft to their nefarious influence. Legends arose that powerful individuals, like the magician Merlin, had a fiendish heritage. Tenacious in their appeal to poets and songsmiths, the allure of the incubi has endured in folklore and popular songs down to the present day.