Demeter had but one daughter, and she needed no other, for Persephone was the Spirit of Spring. The Lord of Shadows and Death, Hades himself, the Unseen One, carried her off in his jet-black chariot, driven by coal-black steeds, through a crevice in the surface of Earth, down the the realms of the dead...
With Zeus' help, the mother retrieved her daughter, but Persephone had already eaten a pomegranate seed, food of the dead, at Hades' insistence, which meant that she must come back to him. In the end, a sort of truce was arranged. Persephone could return to her sorrowing mother but must spend a third of each year with her dark Lord. Thus, by the four-month death each year of the goddess of springtime in her descent to the underworld, did winter enter the world. And when she returns from the dark realms she always strikes earthly beings with awe and smells somewhat of the grave.
— intro. "The Way They Came"
from Sailing The Wine-Dark Sea: Why The Greeks Matter by Thomas Cahill