According to the Cambridge Ritualist, Jane Ellen Harrison, in ancient Greece, there were two different categories of deities, the Olympian (or “heavenly”) and the Chthonian (or “earthly”). The Olympian deities included most of the gods and goddesses which are familiar to students of classic mythology, like Zeus and Hera. These were the gods that lived “in the sky” on Mount Olympus. But there were other gods, who lived under the earth, the chthonic gods. The word “chthonic” comes from the Greek chthonios, meaning “under the earth”. In ancient Greek religion, the chthonic region was at once a source of abundance and death, just as the earth is the womb and the tomb of all life. As Walter Burkert explains:
“the terror of destruction is only one side of the chthonic power. For as long as the land has been tilled, it has been known that food and hence life grows from the depths of the earth: ‘the corn comes from the dead’. Hades is also Pluto, the guardian and giver of wealth in corn; and the corn mother Demeter is in a very special sense the Chthonia in whose care the dead too are hidden.”
Therefore, the Chthonians were simultaneously associated with the source of life and with death, in contrast to the Olympians who avoided all contact with death as a pollution of their immortality.
In addition, there were other deities or spirits, called “daimones”, who were distinct from the gods (theoi) who also inhabited the chthonian realm. According to Jane Ellen Harrison, the belief in these daimones or spirits predated the worship of the Olympian gods. The daimones should not be confused with the Christian conception of “demons”. Greek daimones were not necessarily malevolent. They were forces of nature, and as such could be creative (eudaimon) or destructive (kakodaimon). W.K.C. Guthrie explains that most of the chthonian daimones were tied to the soil of a specific locality in a way that the universalized Olympians were not. Martin Nilsson writes that every field had its last sheaf and its corn-mother and every stone-heap had its daimon living there. Over time, as city-states became cultural centers, the worship of the more universalized Olympians eclipsed the worship of the daimones.
Jane Ellen Harrison contrasted these two traditions of Greek religion, the “Chthonian” and the “Olympian” (Harrison’s contemporary, Francis Cornford used the terms “Dionysian” and “Apollonian”). Each had a distinct attitude toward death and life. Chthonian religion conceived of immortality as the perennial renewal of life in perpetual cycle of death and rebirth (palingensia), while Olympian religion conceived of immortality as deathlessness (athanasia), a life that negates change and death. In the Chthonian view, there is no life without death. Life is a perennial stream which flows in an endless round, a wheel divided into two hemicycles of light and darkness. This view rejects the fixed and changeless immortality which Olympian religion ascribed to its gods. There is only one Life, which like fire is perpetually dying, dying and transforming and being reborn again. Every birth is equally a death, and every death a birth. Thus, the continuity of Life is not broken by death, it is renewed.
“All this, all life and that which is life and reality — Change and Movement — the Olympian renounces. Instead he chooses Deathlessness and Immutability — a seeming Immortality which is really the denial of life, for life is change. … He will not rise again, but chooses instead a barren immortality. … the Olympian who will not die to live renounces life, he desiccates and dies. Such is the very nature of life that only through the ceaseless movement and rhythm of palingesesia is immortality possible. Athanasia, eternity through not dying, is almost a contradiction of words.”
Neo-Paganism is an example of a Chthonian religion, while Christianity is an example of an Olympian religion.