Pagan Lore
Autumn Equinox is a ritual occasion marking the beginning of the fall season, a day when the periods of day and night are of equal length. In mainstream Wiccan mythology the Autumn Equinox marks the time of the Descent of the Goddess into the Underworld. With Her departure we see the decline of Nature and the coming of winter. This is a classic ancient mythos also reflected in the Sumerian myth of Inanna and in the ancient Greek and Roman legends of Demeter and Persephone.
In modern Celtic Wicca/Witchcraft, the Autumn Equinox also bids farewell to the Harvest Lord who is the mythos of some Traditions was slain at the time of Lughnasadh (a Festival marking the beginning of the Celtic harvest season.). Many modern Wiccans refer to the Autumn Equinox as Mabon, named for a legendary Celtic figure who was abducted and imprisoned in the basement dungeon of an enchanted castle. Through this mythos, modern Celtic Witches have established a connection to the traditional Underworld association connected with the Autumn Equinox.
In Italian Witchcraft, the Autumn Equinox marks the slaying of the Harvest Lord, and the resulting descent of the Goddess to find her lost love. The Eleusinian Mysteries, originating in Greece, involve themes of descent and ascent, loss and regain, light and darkness, and the cycles of life and death. Rites associated with these Mysteries were performed at midnight during the Spring and Autumn Equinoxes. This Mystery Tradition spread to Rome and to Britain where initiations into this mythos were given.