Demeter is the goddess of farming, grain and the fertility of the earth. It was she who taught humans to cultivate the fields. To the Romans she was Ceres, from which the word cereal comes. Her most famous myth is that of her daughter Persephone, also called Kore, "the maiden".
The abduction of Persephone
Persephone, daughter of Demeter and Zeus, was picking flowers in a meadow with the nymphs when the earth suddenly opened: Hades, king of the underworld, rode out in his black chariot and carried her off to be his bride, with Zeus's permission. Demeter heard her daughter's last cry and searched the whole world for nine days and nine nights, torch in hand, without eating or sleeping. Only Helios, the Sun, who sees everything, told her the truth.
The earth without harvests
Desperate and furious, Demeter left Olympus and hid among humans at Eleusis, disguised as an old woman. The earth stopped bearing fruit: seeds did not sprout, fields lay bare, people starved and the gods received no more sacrifices. So Zeus sent Hermes to the underworld to bring Persephone back.
The pomegranate seeds
Before letting her go, Hades gave her a few pomegranate seeds to eat. Whoever eats the food of the underworld is bound to it forever, so a compromise was found: Persephone would spend part of the year with her husband as queen of the underworld, and the rest with her mother on earth.
The Eleusinian Mysteries
At Eleusis, in Attica, the Eleusinian Mysteries were celebrated, the most important religious rites of ancient Greece, dedicated to Demeter and Persephone. They were secret: initiates could not reveal what happened, and even today we know only part of it. They promised a better life after death. The sanctuary can still be visited, about 20 km from Athens.
See also the Greek underworld and the twelve gods.