Autumn Equinox is 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, seen the Sumerian myth of Inanna and in the ancient Greek and Roman legends of Demeter and Persephone.
In September, we also bid farewell to the Harvest Lord who was slain at Lammas. He is the Green Man, seen as the cycle of nature in the plant kingdom. He is harvested and his seeds are planted into the Earth so that life may continue and be more abundant.
Mabon ("Great Son") is a Welsh god. He was a great hunter with a swift horse and a wonderful hound. He may have been a mythologized actual leader. He was stolen from his mother, Modron (Great Mother),when he was three nights old,but was eventually rescued by King Arthur (other legends say he was rescued by the Blackbird, the Stag, the Owl, the Eagle, and the Salmon).
All along, however, Mabon has been dwelling, a happy captive, in Modron's magickal Otherworld -- Madron's womb. Only in this way can he be reborn. Mabon's light has been drawn into the Earth, gathering strength and wisdom enough to become a new seed. In this sense, Mabon is the masculine counterpart of Persephone -- the male fertilizing principle seasonally withdrawn. Modron corresponds with Demeter.
From the moment of the September Equinox, the Sun's strength diminishes, until the moment of Winter Solstice in December, when the Sun grows stronger and the days once again become longer than the nights.
Symbols celebrating the season include various types of gourd and melons. Stalk can be tied together symbolizing the Harvest Lord and then set in a circle of gourds. A besom can be constructed to symbolize the polarity of male and female. The Harvest Lord is often symbolized by a straw man, whose sacrificial body is burned and its ashes scattered upon the earth. The Harvest Queen, or Kern Baby, is made from the last sheaf of the harvest and bundled by the reapers who proclaim, "We have the Kern!" The sheaf is dressed in a white frock decorated with colorful ribbons depicting spring, and then hung upon a pole (a phallic fertility symbol). In Scotland, the last sheaf of harvest is called the Maiden, and must be cut by the youngest female in attendance.