Darwin.
At the entrance of the place of torments was an enormous vestibule, tenanted by black Anxieties, Regrets, Groans, Remorse, pale Malady, Decay, Fright, Hunger, Poverty, Death, Sleep, fierce Joy, Rage, and the Eumenides, or Furies, who were seated on a couch of iron, and crowned with blood-stained serpents. A deep and dark cavern led towards Tartarus, which was surrounded by the river Acheron; Charon conducted over this water the souls of those sent to him by Death, while any to whom the rites of sepulchre had not been granted, were for a hundred years allowed to solicit their passage in vain. If any living person presented himself to cross the lake, he could not be admitted before he showed Charon a golden bough; and Charon was once imprisoned for a year, because he had ferried Hercules over without this passport.
Cerberus, a dog with three heads, watched at the entrance to Tartarus.
"A horrid dog and grim, couched on the floor,
Guards, with malicious art, the sounding door;
On each, who in the entrance first appears,
He fawning wags his tail, and cocks his ears;
If any strive to measure back the way,
Their steps he watches, and devours his prey."
Hesiod.