all Greeks as Dionysus of the Trees, sometimes represented as just an upright post (which is considered a phallic symbol). Dionysus assumed the form of a goat, as was Pan, and was worshipped under the title The One of the Black Goatskin; he himself was sacrificed in the shape of a kid in the autumn festival (which marks the end of the year in Mediterranean countries). As God of the Forest, Dionysus can be identified with the King of the Wood at Nemi. At Diana’s grove there, he was her mate and her yearly sacrificial victim, because “some peoples preferred to kill the king while he was still in the full vigor of life.”
In an elaborate site explaining the essence of some Greek deities (s. link below), it is said about Dionysus: He was associated with death and rebirth; (the Great Goddess) Hera arranged for the Titans to kill him and they ripped him to pieces, while the (Earth) goddess Rhea (also known as Cybele) brought him back to life, and he was raised by the mountain nymphs. The followers of Dionysus worshipped him in the woods, working themselves up into mad states of frenzy and ecstasy, and any animals (or people) they came upon would be ripped apart in sacrifice, their flesh eaten raw. In art he is depicted wearing a crown of ivy, and covered in vine leaves and grapes, a typical image of the Green Man. He is a God of Nature and Lord of the Harvest, a God of the Underworld, a Son/Lover of the Goddess, a Child of Promise, the Green Man and the Horned God, all combined into one. The Green Knight of the poem, then, represents this ancient God of the Forest, who was sometimes brother to the Sun god. His being torn to pieces in his sacrifice is symbolized in the poem by being decapitated; his staying alive shows him as the