Pliny’s Natural History (XXV.47) contains a passage that discusses hellebore, a medicinal plant that in ancient times was used to treat insanity. One variety of hellebore, he says, is called melampodion, a name acquired from a shepherd named Melampus, who noticed that the plant had a purgative effect on his female goats (capras purgari pasto illo animadvertentem) once they had eaten it. This milk, we are told, cured “the daughters of Proetus of madness.” Pliny even describes a detailed ritual supposedly used to collect the plant. But who were the daughters of Proetus? What story is being referenced?