The myth is told most completely in the Homeric Hymn to Demeter (c.650 BCE) — one of the oldest and most beautiful texts in Greek literature. Persephone is gathering flowers in a meadow — narcissus, roses, violets, irises — when the earth opens and Hades rises in his chariot to abduct her. She cries out; only Hecate and the sun god Helios hear her. Hades carries her down into the underworld.
Demeter — goddess of grain, Persephone's mother — hears her daughter's cry and searches the earth for nine days and nights without eating, drinking or bathing. On the tenth day she encounters Hecate, who tells her she heard Persephone's cry but did not see the abductor. Helios reveals the truth. Demeter's grief is total and cosmically consequential: she withdraws her gifts from the earth. The grain stops growing. The animals stop bearing young. The earth becomes barren. Humanity begins to starve. The gods receive no sacrifices.
Zeus is forced to act. He sends Hermes to the underworld to bring Persephone back. Hades agrees — but before she leaves, he gives Persephone a pomegranate seed (or seeds — versions vary between one and seven). She eats it. Because she has eaten the food of the dead, she cannot leave permanently. The compromise Zeus negotiates: Persephone will spend part of each year with Hades in the underworld and part with her mother on earth. When she is below, Demeter mourns and the earth is barren — winter. When she returns, Demeter rejoices and the earth flowers — spring and summer.
The pomegranate seed is the myth's most psychologically significant detail. The standard reading — that Hades tricked Persephone — is complicated by the Hymn itself, which is ambiguous about whether she ate knowingly. Many modern readings suggest she ate deliberately — that some part of her chose to remain, chose the depth and the sovereignty of the underworld over the eternal spring of girlhood. The Queen of the Dead cannot be a maiden forever; the pomegranate is the price and the proof of transformation.