Eurytheus ordered Hercules to steal Cerberus from the Underworld. Procede!! Iter difficile est.
Cerberus is the son of Echinda and Typhon, who even the gods were afraid of. He had three dog heads, snake heads all over his back, and a dragon or serpent for a tail. He kept the living out of the dead's underworld. Cerberus praecipuus et periculosum est.
Hercules decided to take some precautions to make sure that he would be able to come back from the Underworld. Hercules went to see Eumolpus, the priest who began the Eleusinian Mysteries. It was believed that if you knew the mysteries, you would be happy in the Underworld. Heracles advenit pro Eumolpo.