The ouroboros, from Greek oura, tail, and a root for eating, is a serpent or dragon curved into a circle, swallowing its own tail. Its earliest known appearance is Egyptian: a coiled serpent encircling the sun-god appears in a funerary text in the tomb of Tutankhamun in the fourteenth century BCE, framing the regeneration of the sun. The figure passed into the Greco-Roman world and was taken up by Hellenistic and Gnostic thought as an image of the cosmos, glossed in a Greek magical text as hen to pan, the all is one. Its consistent meaning across these settings is cyclicality, eternity, the eternal return, the unity in which end feeds beginning.
The Chrysopoeia of Cleopatra, the drawing that pairs the ouroboros with the words hen to pan, survives only in a tenth-century Byzantine manuscript copy, so while the composition is usually attributed to a much earlier Greco-Egyptian alchemical tradition, the physical evidence for the image is medieval rather than ancient, a gap worth keeping separate from the age of the underlying idea. Norse mythology's Jormungandr, the serpent encircling the world and biting its own tail, whose release is bound up with Ragnarok, arrives at a visually similar figure through an entirely unrelated tradition, a reminder that more than one culture reached the same image independently. Gnostic use of the ouroboros on gemstones from the Roman period frequently paired the serpent with Greek letters spelling the sun god's name arranged around its body, tying it to solar cycles and to the boundary between the material cosmos and a higher reality beyond it.