Cerberus

Hesiod's Theogony places Cerberus within a whole family of monsters born to Typhon and Echidna, siblings that include Orthus, the two-headed hound who guards Geryon's cattle in a separate labour of Heracles, the multi-headed Lernaean Hydra, and the fire-breathing Chimera, so that the Twelve Labours as a group amount to Heracles working his way through nearly one monstrous family's entire membership rather than facing a series of unrelated dangers.

Cerberus's later literary afterlife is dominated by Dante. In the sixth canto of the Inferno he guards the third circle of Hell, where the gluttonous lie in freezing mud and filth, and Dante gives him a grotesquely physical presence, three canine heads, clawed hands rather than paws, and a belly he uses to flay the damned, closely modelled on the classical hound but recast entirely within Christian punishment. Virgil, as Dante's guide within the poem, pacifies the beast by throwing fistfuls of earth into its three mouths, a direct medieval echo of the honeyed, drugged cake the Sibyl uses to quiet Cerberus in the Roman Virgil's own Aeneid, so that one ancient poet's trick for getting past the hound becomes, centuries later, a scene within another poem in which Virgil himself repeats it as a character.

The sources do not agree on the hound's anatomy. Hesiod gives fifty heads. The number that stuck is three, which is what the vase painters use and what later poets assume, though two is common in archaic art and probably reflects the practical difficulty of drawing three. A serpent for a tail, and snakes along the back, are frequent additions rather than fixed features.

What is consistent is the job. Cerberus is not there to stop the living entering; several people enter. He is there to stop the dead leaving, and every account of getting past him is an account of a trick rather than a fight. Orpheus plays until the dog sleeps. The Sibyl in the sixth book of the Aeneid throws a drugged honey cake. The offering of honey cakes to the dead, attested as an actual practice, sits behind that detail, so the poem is describing a rite and not inventing a stratagem.

Heracles is the exception and the exception is defined as such. His twelfth labour is to bring the hound up alive, without weapons, and then take it back. He wrestles it. The point of the labour is that it is the one thing a mortal should not be able to do, which is why it comes last and why the dog is returned rather than kept.