And ready-witted Prometheus he bound with inextricable bonds, cruel chains, and drove a shaft through his middle, and set on him a long-winged eagle, which used to eat his immortal liver but by night the liver grew as much again every day as the long-winged bird devoured in the whole day. That bird Herakles, the valiant son of shapely-ankled Alcmene, slew; and delivered the son of Iapetus from the cruel plague, and released him from his affliction -

-Theogony