Hesiod says fifty heads. Pindar says a hundred. Horace, in one ode, gives him a hundred snakes around his head and three tongues; in another, three heads. Apollodorus settles on three heads plus a serpent's tail plus snakes' heads along his back. Sophocles calls him simply the dog with no number at all.
The three-headed version everyone pictures is the artists' compromise, and you can see why: fifty heads cannot be painted on a pot. Three fits on a vase, reads instantly, and gives the animal a legible silhouette. Occasionally archaic art even gives him two, which fits a profile view better still. The count is a practical problem in image-making that hardened into a fact.
What the job actually is
He is usually described as guarding the dead, which is imprecise. Hesiod is specific: he fawns on those who come in, wagging his tail and dropping his ears, and does not let them out again. He is not a gate guard keeping people from entering. He is the reason the dead stay dead.
That inversion — friendly on the way in, lethal on the way out — is the most interesting thing about him, and it is regularly lost in modern versions, which cast him as a snarling obstacle in the entrance hall.
His parents are Typhon and Echidna, which makes him a sibling of the Hydra, the Chimera and Orthrus, the two-headed dog of Geryon that Heracles also killed. He belongs to a single family of monsters that a hero is expected to clear out.
The twelfth labour
Hauling him up alive is the last and hardest of the labours, and it is the only one that takes Heracles out of the world entirely. Apollodorus gives the fullest version: he is initiated into the Eleusinian Mysteries first, as preparation; he goes down at Taenarum in Laconia; Hades grants permission on the condition that he take the dog without weapons. So he wrestles it, wearing his lion skin, gets his arms round its neck and squeezes until it submits, and carries it up. Eurystheus, seeing it, hides in his storage jar again and asks him to take it back.
The rock Cerberus was brought up at was pointed out in several places — Taenarum, Troezen, Heraclea Pontica on the Black Sea. At Heraclea, Ovid and others report, the dog's slaver dripped onto the ground and produced aconite, wolfsbane, which is a genuinely deadly plant and grows in that region. That is a good example of a myth being anchored to a local botanical fact.
Getting past him
Every descent has to solve him, and the solutions are a small catalogue of Greek problem-solving.
- Orpheus plays. The music puts him to sleep — Virgil in the Georgics has the three mouths gape in astonishment.
- The Sibyl in Aeneid 6 throws a drugged honey-cake, and the dog eats it and sprawls out across the whole cave. The Roman idiom "a sop to Cerberus" comes from this passage, and honey-cakes were genuinely placed in some graves.
- Psyche, in Apuleius, is given two cakes for the journey down and back, one for each direction, and warned not to let go of them.
- Heracles simply chokes him, because that is what Heracles does.
- Aeneas does not have to; the Sibyl handles it.
The pattern is worth noticing: everyone else uses music, food or magic. The strength solution is available to exactly one person.
Where the name comes from
Kerberos has been connected, in a much-discussed but contested proposal, to a Sanskrit word śabala, "spotted", the epithet of one of the two dogs of Yama, the Vedic lord of the dead — which would make the hell-hound an inherited Indo-European figure with a shared name. The sound correspondences do not work cleanly and the etymology is not accepted by everyone. Other proposals derive the name from a word for the pit, or treat it as pre-Greek.
Whether or not the linguistics holds, the comparative pattern is real: guardian dogs at the entrance to the land of the dead appear in Indian, Iranian and Norse material, and dogs are associated with death and thresholds across a wide area — including in Greece with Hecate, whose animal is also the dog.
In Dante, Hades and everywhere else
Dante puts him in the third circle, guarding the gluttons, tearing at them in the freezing rain, and Virgil quiets him with a handful of earth — a deliberate parody of the honey-cake. Blake and Doré both drew him. Rubens painted the Heracles episode.
Modern reception is enormous and mostly affectionate. He is the Harry Potter books' Fluffy, put to sleep by a harp exactly as Orpheus did it — an explicit borrowing. He is a boss in nearly every mythology-based game and a mount, pet or ally as often as an enemy; the Hades game makes him a good dog the player can pet. He gives his name to computer security's Kerberos authentication protocol, developed at MIT in the 1980s, on the logic that it originally had three components: client, server and authenticator.
His only serious modern loss is the direction of travel. Almost every version has him keeping people out.
Head-counts, honey-cakes, and a brother dog
Does he ever appear apart from a hero's descent?
Rarely. He is essentially a fixture rather than a character: mentioned when someone is going down or coming up, and otherwise at his post. Aristophanes' Frogs gets comedy out of Dionysus' terror of him without actually bringing him on stage. That immobility is his function; a guard who wanders is not doing the job.
What did he look like in Greek art?
Usually a large dog of ordinary build — the Laconian hound type, not a monster of unusual size — with two or three heads and often a snake for a tail or serpents rising from his back and neck. The Heracles-and-Cerberus scene is common on Attic vases from the sixth century BCE and the tone varies from grim to nearly comic, with the dog sometimes shrinking backwards. He is not usually given fire, spikes or the massive scale that modern illustration prefers.
Is Orthrus a separate dog?
Yes, and an under-appreciated one: two heads, brother of Cerberus, guardian of the cattle of Geryon in the far west, killed by Heracles with a single blow of the club during the tenth labour. Hesiod also makes him, disturbingly, the father of the Sphinx and the Nemean lion by his own mother Echidna. Two monstrous dogs at opposite edges of the world, both killed by the same hero, is a symmetry the tradition seems to have enjoyed.
What is the honey-cake actually about?
Cakes of honey and grain were real Greek and Roman grave offerings, placed with the dead, and the melitoutta given to Cerberus in Roman sources is a specific named item. So the literary detail reflects an actual burial practice, and the practice may well have been understood by ordinary people as provisioning the dead for exactly the encounter the poets describe — in the same way as the coin for Charon. That makes the underworld's two gatekeepers the parts of Greek eschatology most visible in the archaeological record.