Ouroboros

from wikipedia:

The Ouroboros or Uroborus[1] is an ancient symbol depicting a serpent or dragon swallowing its own tail and forming a circle.

The Ouroboros often represents self-reflexivity or cyclicality, especially in the sense of something constantly re-creating itself, the eternal return, and other things perceived as cycles that begin anew as soon as they end (compare Phoenix). It can also represent the idea of primordial unity related to something existing in or persisting from the beginning with such force or qualities it cannot be extinguished. The ouroboros has been important in religious and mythological symbolism, but has also been frequently used in alchemical illustrations, where it symbolizes the circular nature of the alchemist's opus. It is also often associated with Gnosticism, and Hermeticism.

Carl Jung interpreted the Ouroboros as having an archetypal significance to the human psyche.[citation needed] The Jungian psychologist Erich Neumann writes of it as a representation of the pre-ego "dawn state", depicting the undifferentiated infancy experience of both mankind and the individual child.[2]

Alchemy

In alchemy, the Ouroboros is a purifying sigil. Swiss psychologist Carl Jung saw the Ouroboros as an archetype and the basic mandala of alchemy. Jung also defined the relationship of the Ouroboros to alchemy:[6]

The alchemists, who in their own way knew more about the nature of the individuation process than we moderns do, expressed this paradox through the symbol of the Ouroboros, the snake that eats its own tail. The Ouroboros has been said to have a meaning of infinity or wholeness. In the age-old image of the Ouroboros lies the thought of devouring oneself and turning oneself into a circulatory process, for it was clear to the more astute alchemists that the prima materia of the art was man himself. The Ouroboros is a dramatic symbol for the integration and assimilation of the opposite, i.e. of the shadow. This 'feed-back' process is at the same time a symbol of immortality, since it is said of the Ouroboros that he slays himself and brings himself to life, fertilizes himself and gives birth to himself. He symbolizes the One, who proceeds from the clash of opposites, and he therefore constitutes the secret of the prima materia which [...] unquestionably stems from man's unconscious.

The famous Ouroboros drawing from the early alchemical text The Chrysopoeia of Cleopatra dating to 2nd century Alexandria encloses the words hen to pan, "one is the all". Its black and white halves represent the Gnostic duality of existence. As such, the Ouroboros could be interpreted as the Western equivalent of the Taoist Yin-Yang symbol.

The Chrysopoeia Ouroboros of Cleopatra is one of the oldest images of the Ouroboros to be linked with the legendary opus of the Alchemists, the Philosopher’s Stone.

As a symbol of the eternal unity of all things, the cycle of birth and death from which the alchemist sought release and liberation, it was familiar to the alchemist/physician Sir Thomas Browne. In his A letter to a friend, a medical treatise full of case-histories and witty speculations upon the human condition, he wrote of it:

[...] that the first day should make the last, that the Tail of the Snake should return into its Mouth precisely at that time, and they should wind up upon the day of their Nativity, is indeed a remarkable Coincidence,

It is also alluded to at the conclusion of Browne's The Garden of Cyrus (1658) as a symbol of the circular nature and Unity of the two Discourses:

All things began in order so shall they end, so shall they begin again according to the Ordainer of Order and the mystical mathematicks of the City of Heaven.