Eurystheus wanted Herakles to bring him three golden apples. Herakles set off. The river god Nereus refused to give him directions and changed his shape again and again. Herakles tied him to a tree until he told the way. In the Caucasus, Herakles freed the Titan Prometheus, the fire-bringer, from his chains. Prometheus warned Herakles not to pick the apples himself, but to ask someone else to do it.