Before the gods, the earth bore monsters with a single eye burning in the middle of the brow. In the oldest layer of the Greek theogony, Sky ruled the world, wedded Earth, and "Earth bore him the Cyclopes" — three of them, "Arges, Steropes, Brontes,' of whom each had / one eye on his forehead". Their father, fearing such children, bound them and "cast into Tartarus, a gloomy place in Hades"; the single eye is thus the first monstrous feature the cosmos produces, older than the Titans, older than Zeus. This is the account preserved in Apollodorus's Library (a Greek mythography compiled in the 1st–2nd century CE), which sets the one-eyed smiths at the very hinge where sky and earth divide.

The same forehead-eye stares out of a wholly different tradition. Myths & Legends of China (published 1922) surveys a land of "the One-eyed People" whose single eye is "placed in the centre of the forehead, directly / above the nose"; and in the neighbouring Land of the Flying Cart the inhabitants have one arm and "an additional eye of large size in / the centre of the forehead, / making three eyes in all", riding wheeled carts that chase one another through mid-air. Greek terror and Chinese whimsy converge on the identical anatomy — the eye set where a third ought never to be.

Stith Thompson (1885–1976), the American folklorist whose motif-index gives this shape its number, cross-referenced it to the Irish Balor and to Icelandic and Indian analogues, and the Greek witness reaches us through the editor Sir James Frazer (1854–1941), whose notes accompany the Library — though here the primary text speaks plainly enough on its own. Only the Greek and Chinese witnesses are wired to served text; the Celtic and Indian authorities wait unread. Why does the imagination so often place its wonders and its horrors at the same single point above the nose?