The incarnation of the demons has been a problem to Christian demonology and theology since early times. A very early form of incarnation of demons was the idea of demon possession, trying to explain that a demon entered the body of a person with some purpose or simply to punish that one for some allegedly committed sin. But this soon acquired bigger proportions, trying to explain how demons could seduce people to have sexual relationships with them or induce them to commit other sins. To Christian scholars demons had to manifest themselves in a visible and if possible tangible form.

Basil of Caesarea was, apparently, the first who wrote on this subject. He believed that demons, to materialise, had to condense vapours and with them form the body of a person or animal, then entering that body as if it were a puppet to which they gave life. Henry More supported this idea, saying that their bodies were cold due to the solidification of water vapour to form them (see below). Many authors believed that demons could assume the shape of an animal, preferably black.

It seems that until the first millennium, when the fear for the coming of the Antichrist reached proportions that were out of control, the appearance of demons was not a significant problem. But since this moment on, demons acquired a terrible appearance in the mind of those who believed to have seen them.

Raoul Glaber, a monk of Saint-Léger, Belgium, seems to have been the first in writing about the visit of a demon of horrible aspect in his Historiarum suis temporis, Libri quinque (History of his time, Book five).

Augustine thought that demons often were imaginary, but sometimes could enter human bodies, but later accepted the idea of the materialisation of demons. Thomas Aquinas followed Augustine's idea, but added that demonic materialisation had sexual connotations because demons tried to seduce people to commit sexual sins.

Henri Boguet and some English demonologists of the same epoch asserted that witches and warlocks confessed (under torture) that demons' bodies were icy. During the 17th century this belief prevailed.

Concerning the weight of the demons, since the 17th century people affirmed that they were heavier than common humans.

About the colour of the demons' skin, since early times it was associated with black, thinking that they assumed the appearance of a black man, although not all descriptions agreed, giving demons very different aspects.

Ambrogio de Vignati, disagreeing with other authors, asserted that demons, besides of not to have a material body could not create it, and all what they seemed to do was a mere hallucination provoked by them in the mind of those who had made a diabolical pact or were "victims" of a succubus or incubus, including the sexual act.

The demons' behind, genitalia and sperm were a subject of dedicated study by Christian theologians, demonologists and inquisitors. The Inquisition seemed to have been particularly interested in this topic.

Concerning the demons' behind, there were confessions asserting that they were normal, others telling that instead of an anus they had another mouth and thus when kissing their behind during the Sabbath people received another kiss in exchange, and confessions telling that demons did not have buttocks.

About the demons' testicles, only one witch confessed to Pierre de Rostegny that the demon with whom she had sexual relationships had them. Other confessions denied that demons had them. Henri Boguet supported the idea that demons did not have sexual organs and Johann Meyfarth asserted that demons had not a penis.

The demons' penis was a terrible problem for inquisitors and scholars. All of them manifested a morbid interest in the demons' genitalia, but the penis reached pathological proportions. Many questions during the interrogatories in the witch trials referred to this theme. All persons confessed to have had sexual relationships with at least one demon, but the descriptions given of this particular part of their anatomy vary from a small phallus to a big one. Some confessions described a normal penis in the appropriate place, others a normal one in the behind, others two phalluses, one in its place and the other in the behind, and others a bifid one, like the tongue of a snake. Confessions that described two phalluses or a bifid one often added the particularity that the demon practised vaginal and anal coitus at the same time; Sylvester Prieras was a supporter of this idea. Even some confessions described three penises. Concerning the material of which it were made, there were confessions affirming that it was normal and flesh-made, others saying that it was iron or horn-made, others telling that it was half flesh and half iron, and others saying that it had scales and, being scaly, the sexual act was painful; even some confessions asserted that it was bone or wooden-made.

The sperm of the demons constituted another problem. Some persons confessed that this sperm was icy, meanwhile others felt it as that of a common man. But another problem arose among scholars to determine if demons had their own sperm or not. Ludovico Maria Sinistrari was one of the few authors that supported the idea that demons were corporeal entities that had their own sperm and with it could impregnate women and conceive children with them. But most scholars denied the idea that demons could have their own sperm, and concluded that they took sperm from men. The problem grew when these authors had to explain how did demons took that sperm, how did they put it into a woman's vagina, and if that sperm could conceive children or not.

Most theologians agreed in the fact that demons acted first as succubae to collect sperm from men and then as incubi to put it into a woman's vagina. But as many of them agreed also in the fact that demons' bodies were icy, they reached the conclusion that the frozen sperm taken first from a man could not have generative qualities. Albertus Magnus and Thomas Aquinas wrote that demons acted in this way but could fecundate women. Ulrich Molitor and Nicholas Remy disagreed in the fact that women could be impregnated; besides, Remy thought that a woman could never be fecundated by another being than a man. Heinrich Kramer and Jacob Sprenger (authors of the Malleus Maleficarum adopted again an intermediate position; they wrote that demons acted first as succubae and then as incubi, but added the possibility that incubi could receive semen from succubae, but they considered that this sperm could not fecundate women.

Peter of Paluda and Martin of Arles among others supported the idea that demons could take sperm from dead men and impregnate women. Some demonologists thought that demons could take semen from dying or recently deceased men, and thus death men should be buried as soon as possible to avoid it.

There is no biblical mention of the incarnation of demons in the New Testament, but according to the Matthew, Mark and Luke they could be seen and heard (there are several allusions). In the Old Testament Eve saw and heard the Devil incarnated in a serpent (Genesis 3:1-5)

See also