In the myth and folklore of the Near East and Europe, Gello (also Gyllou, Gylou, Gillo, etc.) is one of the many names for a female demon or revenant who threatens the reproductive cycle by causing infertility, spontaneous abortion, and infant mortality.
Aramaic inscriptional evidence of a child-snatching demon appears on a silver lamella (metal-leaf sheet) from Palestine and two incantation bowls dating to the 5th or 6th century; on these she is called Sideros (Greek for iron, a traditional protection for women during childbirth). Under various names, she continues to appear in medieval Christian manuscripts written in Greek, Coptic, Ethiopian, Armenian, Romanian, Slavonic, Syriac, Arabic, and Hebrew. In literary texts and on amulets, the demon's adversaries are Solomon, saints, or angels.
Knowledge of a demon's name was required to control or compel it; a demon could act under an alias. Redundant naming is characteristic of magic charms, "stressing," as A.A. Barb noted in his classic essay "Antaura," "the well-known magic rule that the omission of a single one can give the demons a loophole through which they can work their harm."
|“||My first and special name is called Gyllou; the second Amorphous; the third Abyzou; the fourth Karkhous; the fifth Brianê; the sixth Bardellous; the seventh Aigyptianê; the eighth Barna; the ninth Kharkhanistrea; the tenth Adikia; (…) the twelfth Myia; the half Petomene.||”|
Elsewhere, the twelve-and-a-half names are given as Gylo, Morrha, Byzo, Marmaro, Petasia, Pelagia, Bordona, Apleto, Chomodracaena, Anabardalaea, Psychoanaspastria, Paedopniktria, and Strigla. Although magic words (voces magicae) have often been corrupted in transmission or deliberately exoticized, several of these names suggest recognizable Greek elements and can be deciphered as functional epithets: Petasia, "she who strikes"; Apleto, "boundless, limitless"; Paedopniktria, "child suffocator." Byzo is a form of Abyzou, abyssos, "the Deep," to which Pelagia ("she of the sea") is equivalent.
Gello is named also in works by the polymaths John of Damascus (7th–8th century) and Michael Psellos (11th century), the latter of whom notes that he has found her only in "an apocryphal Hebrew book" ascribed to Solomon and not in his usual sources for demonic names in antiquity. Psellos was one of the earliest scholars to identify Gello with the Hebrew Lilith, and says that these demons "suck blood and devour all the vital fluids which are in the little infant." The 17th-century Greek Catholic scholar Leo Allatios, however, criticizes Psellos and insists that the gello, Lilith and other demonic creatures should be regarded as separate and unrelated.
Walter Burkert derived Gello from the Near Eastern demon Gallu. M.L. West also pointed to the Babylonian–Assyrian gallû, a word perhaps related to "ghoul," as a demonic revenant who brings sickness and death.
Because etymology in antiquity was interpretive and phonic, and not based on scientific linguistics, the Greeks themselves might have heard the root gel-, "grin, laugh," in the sense of mocking or grimacing, like the expression often found on the face of the Gorgon, to which Barb linked the reproductive demons in origin. Such demons are often associated with or said to come from the sea, and demonologies identify Gyllou with Abyzou, whose name is related to abyssos, the abyss or "deep."
Gello appears in Greek sources as one of three reproductive demons who developed as a persona with an individual story of origin (aition). The fears she personifies thus associate her with the Mormo and Lamia, whose narratives also show them to have suffered the fate that they in turn inflict on other women. Mormo, driven to insanity, killed and ate her own children; Lamia was the lover of Zeus and bore him many children, but Hera in her envy killed each as it was born.
Gello was once a young woman who died a virgin. The Christian-era lexicographer Hesychius said that she was a ghost (eidolon) who attacked both virgins and newborn babies. The earliest mention of this demonic creature by her Greek name occurs in a fragment of Sappho of Lesbos, in which Gello is said to be "fond of children." The fragment is preserved by the 2nd-century compiler Zenobius, who offers a psychological explanation:
|“||'Fonder of children than Gello' is a saying applied to women who die prematurely (aôrôs), or to those who are fond of children but ruin them by their upbringing. For Gello was a maiden (parthenos), and because she died prematurely (aôrôs), the Lesbians say that her ghost haunts little children, and they also blame her for the deaths of those who die prematurely (aôrôn).||”|
Magic texts and amulets attest by name to the prevalence of a belief in reproductive demons in the Greco-Roman world. During the Byzantine period, textual evidence of the child-harming demon is most often found in exorcisms or demonologies. Historian of ancient religion Sarah Iles Johnston suggests that this belief is expressed more commonly in earlier literature than has been noticed. The Homeric epics allude to the unmarried dead, who are excluded from the Underworld and might harm the living. In the Homeric Hymn to Demeter, Demeter in her role as a kourotrophic ("youth-nurturing") goddess promises to protect her hosts' infant from demonic attack in language that recalls known magical incantations. Centuries later, in Augustan Rome, Ovid describes the practice of protecting doorways with buckthorn after the birth of a child to ward off striges, winged female demons who were thought to suck the blood of newborns. One of the twelve-and-a-half names of Gylo (see above) is Strigla, a form of the word strix as a kind of witch.
Michael Psellos says that Gello also killed pregnant women and their fetuses. Thus Gello in general blocked the cycle of reproduction. The patriarch John of Damascus, in the treatise Peri strygnôn ("Regarding striges"), records a belief among the "common people," still current in his day, that ghosts called gelloudes or striges flew nocturnally, slipped into houses even when the windows and doors were barred, and strangled sleeping infants. John's use of the plural shows that Gello has become a type, rather than an individual revenant. The 14th-century Greek ecclesiastical historian Nikephoros Kallistos Xanthopoulos said gelloudes "bring the infant from the bedroom, as if about to devour him." Leo Allatios explicitly cross-identifies striges and gelloudes, recasting the demonic or revenant gello of Eastern tradition as the witch of Western Europe, who is often marginalized by age and poverty. The transformation of the gello from the ancient "virginal reproductive demon" to an envious crone occurs in the Christian era; what the virgin and crone share is their exclusion from the reproductive cycle, and their envy of fertility. The Greek folk belief continued into the modern era. 
Although reports of Gello's behavior are consistent, her nature is less determinate. She is regarded as a demon in exorcisms and commanded as an "unclean spirit" (akatharton pneuma). But her aition as a human being would make a ghost of her, as did her gendered nature, since demons, like angels, were officially sexless in the theology of the Church. Johnston prefers to use the Greek word aôrôs, "untimely dead," for this form of transgressive or liminal soul or entity, finding the usual phrase "child-killing demon" to be misleading.
The late antique magico-medical compilation Cyranides provides defensive spells against the "frightful woman" (horrida mulier) who attacks babies. The eagle-stone or aetites is to be worn as an amulet to prevent miscarriage, to assure timely and complication-free delivery, and to relieve delirium and night terrors associated with Gello and other revenants. A cross or image of Christ might be placed by a child's bed to ward off Gello or demons in general; burning lamps to illuminate sacred images and incense were also used in the bedroom. The practice of baptizing infants was thought to offer protection against demon-snatching, and specifically against the gello, according to Leo Allatios. Allatios also records, but does not condone, the hanging of red coral or a head of garlic on the infant's cot, along with other remedies he finds too unspeakable to name.
In Byzantine sources, the adversary of Gello is often St. Sisinnius or Sisoe, whose defeat of her is his most renowned deed. On amulets, Sisinnius is depicted as a horseman bearing down with his spear on the female demon, who has fish- or serpent-like attributes below the waist. In one Byzantine folktale, Gello slips into a heavily guarded castle by disguising herself as a fly on the saint's horse, since only Sisinnius could pass through the gate.
There is an Ethiopian tradition in which the sister of Sisinnius was possessed by a demon and killed newborns. When Sisinnius became a Christian, he murdered her. In a Byzantine version, Sisinnius defends his sister Melitene's children from the demon Gyllou. A sample narrative of Melitene's travails against the gelu may be found online.
A 15th-century manuscript describes an encounter between the archangel Michael and Gylou:
|“||The archangel Michael said to her, 'Where have you come from and where are you going?' The abominable one answered and said, 'I am going off to a house and, entering it like a snake, like a dragon, or like some reptile, I will destroy the animals. I am going to strike down women; I will make their hearts ache, I will dry up their milk … I will strangle [their] children, or I will let them live for a while and then kill them' … .||”|
Although the name Gylou is not found on any surviving amulets, Michael is the adversary Gylou encounters most often in medieval Byzantine texts.
Johnston offers an interpretation of the reproductive demons' social significance:
|“||By making Gello a virgin and Lamia and Mormo mothers who had lost their children, myth reiterated the message that a Greek woman's life was defined by successful reproduction and that women who failed to live up to this goal belonged in the dark and marginal world of the restless dead rather than in the human world. … Greek tradition was also normative in that it censured the real acts of killing a child or impeding reproduction. By going further, however, and describing these ghosts as envious — by virtually making them personifications of envy — tradition also censured the envy itself. 'This is where reproductive envy leads,' the myths seem to say, 'to exclusion from humanity and an eternity spent in restless wandering.'||”|
The protections against Gellou, as an embodiment of envy, resemble those against the evil eye. One exorcism text dating from around the turn of the 19th–20th century gives Baskania as a name for the gello as well as for the evil eye.
The psychological aspects of Gello were observed also by Leo Allatios in his work De Graecorum hodie quorundam opinionibus ("On the beliefs of the Greeks today"). Textual sources he collected on the Gello included Sappho's poem, the Suda, exorcisms, a church history, the Life of Patriarch Tarasios of Constantinople written by Ignatius the Deacon, and proverbs. Allatios's purpose was to demonstrate the continuity of customs and morals, but also to show that these beliefs distorted or ran contrary to Christian doctrine. Sometimes the acts characteristic of Gello were attributed to "poor and miserable old crones," who could be accused in court as gelloudes and might even claim or confess to have acted as such. In his Life of Tarasios, Ignatius the Deacon recounts an actual case in which two women were charged as gelloudes and brought before his subject's father, who acquitted them. Penance might be prescribed for confessed gelloudes, and is found specified in a few Nomocanons, or collections of ecclesiastical law. Michael Psellos, however, rejected the notion that human beings could transform into demonic beings, and so there would be no need for a particular penance; the official position of Orthodoxy was that such creatures did not exist.
Despite her official non-existence, the gello is named in exorcisms, which required the attendance of a priest, and in prayer formularies. The Virgin Mary is invoked against the child-harming demon gylo:
|“||Therefore I pray, my Lady, for your swiftest aid, so that the children of these your servants N and N may grow up, and that they may live and give thanks in the sight of the Lord for all the days of their lives. Thus let it be, my Lady. Listen to me, a sinner and unworthy servant and although I am a sinner, do not despise my poor and miserable prayer but protect the children of your servants and let them live and send the Angel of Light so that he may protect and defend them from all evil, from wicked spirits, and from fiends which are in the air, and do not let them be singled out by other <demons> and by the accursed gylo lest harm comes to them and their children.||”|
In one exorcism of the gello, no fewer than 36 saints are invoked by name along with Mary and the "318 Saints of the Fathers", with a final addendum of "all the saints." Some prayers resemble magic spells in attempting to command or compel the saints, rather than humbly requesting aid. Exorcisms emphasize that Christian families deserve exclusive protection. Gello continued to be named in exorcisms into the 20th century.
In early Christianity, a program of exorcism was preliminary to baptism as a kind of purification and to drive away evil spirits, and not necessarily because the person was thought to be possessed. The ambiguous state of the unbaptized is expressed by conflicting views of the infant: that the newborn had not sinned, and that the newborn nonetheless bore the pollution of original sin and was thus closer to the Devil than to God. The travel writer Sonnini de Manoncourt recorded that the Greeks called an unbaptized child drako (or dracon, "serpent, python, dragon"). At baptism, the name Drako is shed and replaced with a Christian name. The names of Gylo include Chomodracaena, containing drakaina, "female dragon." In one text dealing with the gello, she is banished to the mountains to drink the blood of the drako; in another, she becomes a drako and in this form attacks human beings. In other texts, the child itself is addressed as Abouzin (Abyzou).
In ancient and medieval medical texts, a child was thought to be conceived from the father's "seed" and the mother's blood. The gello, herself infertile and envious, aimed to drink blood, the source of fertility, and was attracted to the dangerous time of birth and recovery in part because the new mother was regarded in Judaeo-Christian tradition as unclean; this state of pollution was congenial to demons. As long as the infant remained exclusively within the birth mother's sphere of influence, it was vulnerable to female demons seeking blood. In the story of Melitene, sister of the saints Sisinnios and Sisynodorus, the child is in peril until it is "returned" to the hands of men. In one version, the gello swallows the child and must be forced by the male saints to regurgitate it alive. This cycle — death by swallowing, regurgitation, new life — may be symbolized in initiation ceremonies such as baptism, which marked the separation of the child from the taint of its mother's gello-attracting blood.
Gyllou is featured in a major text of modern Luciferianism, a belief system that venerates Lucifer. In The Bible of the Adversary by Michael W. Ford, she is associated with Lilith and represents Vampyrism as a desire for eternal life.
Scholarly discussions of Gello associate her with and analyze the meaning of her narrative traditions in relation to the following demons and supernatural beings: