Quote from the Encyclopedia Britannica:

It was King Eurystheus who imposed upon Heracles the famous Labours, later arranged in a cycle of 12, usually as follows: (1) the slaying of the Nemean lion, whose skin he thereafter wore; (2) the slaying of the nine-headed Hydra of Lerna; (3) the capture of the elusive hind (or stag) of Arcadia ; (4) the capture of the wild boar of Mt. Erymanthus; (5) the cleansing, in a single day, of the cattle stables of King Augeas of Elis; (6) the shooting of the monstrous man-eating birds of the Stymphalian marshes; (7) the capture of the mad bull that terrorized the island of Crete; (8) the capture of the man-eating mares of King Diomedes of the Bistones; (9) the taking of the girdle of Hippolyte, queen of the Amazons; (10) the seizing of the cattle of the three-bodied giant Geryon, who ruled the island Erytheia (meaning Red) in the far west; (11) the bringing back of the golden apples kept at the world's end by the Hesperides; and (12) the fetching up from the lower world of the triple-headed dog Cerberus, guardian of its gates.
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