Gello (Γελλώ), in Greek mythology, is a female demon or revenant who threatens the reproductive cycle by causing infertility, miscarriage, and infant mortality. By the Byzantine era, the gelloudes (γελλούδες) were considered a class of beings. Women believed to be under demonic possession by gelloudes might stand trial or be subjected to exorcism. Gyllou, Gylou, Gillo, or Gelu are some of its alternate forms. Gello possibly derives from Gallû, an ancient Mesopotamian demon believed to bring sickness and death. The theory was advanced by Carl Frank (1881–1945) and supported by Martin Litchfield West, Walter Burkert, and others. The name is also preserved in the later word ghoul. Greek folk etymology links the word to 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 demons exercising a malign influence on reproduction. 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." According to ancient myth, Gello was a young woman who died a virgin, and returned as a ghost (φάντασμα, phantasma) to do harm to the children of others. The myth is given as an explanation of a proverb by the second-century compiler Zenobius. It is noted that Sappho mentioned her, implying that Gello was a feared bane of children at least as far back as the sixth century BC. The lexicographer Hesychius of Alexandria, who wrote in the fifth or sixth century but drew from earlier lexicons, glossed gello as a ghost (eidolon) who attacked both virgins and newborn babies. Since the Early Middle Ages, Gello has often been conflated with Lamia and Mormo, two similar mythological figures. Each originated as a single individual woman (with her own origin myth or aition) in Ancient Greece, but later developed into a type of frightening apparition or demon. The gello eventually came to be regarded as a type of being, rather than an individual.