In the Middle Ages, people in Europe believed that Incubi (one Incubus, several Incubi) were male demons. There were also female demons, called succubi. They lay on sleeping people, to have sexual intercourse with them. They would also do this to make other incubi. While they had sex with their victim, they drained its energy to sustain themselves. Sometimes, having sex with an incubus may result in a child, as in the legend of Merlin. Some sources say that the incubus may be identified by its unnaturally cold penis. Religious tradition holds that repeated intercourse with such a spirit by either males or females may result in bad health, or even death.
Origins of the legends [change]
People have come up with different explanations for the incubus legends. In the Middle Ages, people worried a lot about sin, especially sexual sins of women. Victims may have been experiencing waking dreams or sleep paralysis. Also, nocturnal arousal, orgasm or nocturnal emission could be explained by the idea of creatures causing an otherwise guilt-producing and self-conscious behavior. The influence of incubi could also have been used to explain how pregnancies happen outside marriage; such pregnancies were often "unexplainable".
Victims who claimed to have fallen prey to the influence of incubi, could in reality have been victims of sexual assault by a real person. Rapists may have attributed the rapes of sleeping women to demons in order to escape punishment. A friend or relative may have assaulted the victim in her sleep. The victims and, in some cases the clergy, may have found it easier to explain the attack as supernatural rather than confront the idea that the attack came from a trusted person.
Ancient and religious descriptions [change]
One of the earliest mentions of an incubus comes from Mesopotamia on the Sumerian kings' list, ca. 2400, where the hero Gilgamesh's father is listed as Lilu (Lila). It is said that Lilu disturbs and seduces women in their sleep, while Lilitu, a female demon, appears to men in their erotic dreams. Two other demons appear as well: Ardat lili visits men by night and bears ghostly children from them. Irdu lili, is the male counterpart to Ardat lili. He visits women by night. These demons were originally storm demons. Because the etymology was interpreted wrongly, they were later seen as night demons. Also considered to be vampires which is another form of a demon that is said to drink blood from its victims.
Incubi and succubi were said by some not to be different sexes, but the same demon able to change its sex. A succubus would be able to sleep with a man and collect his sperm, and then transform into an incubus and use that seed on women. Their offspring were thought to be supernatural in many cases, even if the actual genetic material originally came from humans.
Many tales claim that the incubus is bisexual, but some indicate that it is strictly heterosexual and finds attacking a male victim either unpleasant or detrimental. There are also many stories involving the attempted exorcism of incubi or succubi who have taken refuge in the bodies of men or women.
Incubi are sometimes said to be able to conceive children. The half-human offspring of such a union is sometimes referred to as a cambion. The most famous legend of such a case includes that of Merlin, the famous wizard from Arthurian legend.
According to the Malleus Maleficarum, exorcism is one of the five ways to overcome the attacks of Incubi, the others being Sacramental Confession, the Sign of the Cross (or recital of the Angelic Salutation), moving the afflicted to another location, and by excommunication of the attacking entity, "which is perhaps the same as exorcism."  On the other hand, the Franciscan friar Ludovico Maria Sinistrari stated that incubi "do not obey exorcists, have no dread of exorcisms, show no reverence for holy things, at the approach of which they are not in the least overawed."
- Merlin's father was said to be an incubus in Geoffrey of Monmouth's Historia Regum Britanniae and many later tales. See Lacy, Norris J. (1991). "Merlin". In Norris J. Lacy, The New Arthurian Encyclopedia, pp. 322. (New York: Garland, 1991). ISBN 0-8240-4377-4.
- Russsel, Jeffrey Burton (1972), Witchcraft in The Middle Ages, pp. 239, 235 Cornell University Press, Ithaca and London, ISBN 0-8014-0697-8
- Stephens, Walter (2002), Demon Lovers, p. 23, The University of Chicago Press, ISBN 0226772624
- Lewis, James R., Oliver, Evelyn Dorothy, Sisung Kelle S. (Editor) (1996), Angels A to Z, Entry: Incubi and Succubi, pp. 218, 219, Visible Ink Press, ISBN 0-7876-0652-9
- Masello, Robert (2004), Fallen Angels and Spirits of The Dark, p. 66, The Berkley Publishing Group, 200 Madison Ave. New York, NY 10016, ISBN 0-399-51889-4
- Raphael Patai, p. 221, The Hebrew Goddess: Third Enlarged Edition, ISBN 978-0-8143-2271-0
- Siegmund Hurwitz, Lilith: The First Eve ISBN 978-3-85630-522-2
- Raphael Patai, p. 221 & 222, The Hebrew Goddess: Third Enlarged Edition, ISBN 978-0-8143-2271-0
- Carus, Paul (1900), The History of The Devil and The Idea of Evil From The Earliest Times to The Present Day, "The Devil's Prime," at sacred-texts.com
- Russsel, Jeffrey Burton (1972), Witchcraft in The Middle Ages, p. 145, Cornell University Press, Ithaca and London, ISBN 0-8014-0697-8
- Stephens, Walter (2002), Demon Lovers, pp. 54, 55, 332, 333, The University of Chicago Press, ISBN 0226772624
- Kramer, Heinrich and Sprenger, James (1486), Summers, Montague (translator - 1928), The Malleus Maleficarum, Part2, Chapter 1, "The Remedies prescribed by the Holy Church against Incubus and Succubus Devils," at sacred-texts.com