Ancient Greeks knew that death was the final door they had to cross. After a burial in the Earth, water carried deceased mortals into Hades, the realm of the Underworld. They spent the rest of their existence there until they were ultimately forgotten.

The Greeks’ idea of Hades and what it looked like constantly evolved over time, but one thing was certain: Once you were dead, you could not cross back into the living (and vice versa). The guardian of these barriers between life and the afterlife was none other than the fearsome, three-headed dog-creature we know as Cerberus – Hades’ hellhound.

What Is a Hellhound?

A hellhound is a mythical dog depicted in ancient Greek and Scandinavian mythologies.

Cerberus: The 3 Headed Dog

Born from the monstrous, multi-headed Typhon and the serpent-woman Echidna, Cerberus was among the primordial monsters predating humanity. Poets and artists depict it as a large canine beast with three, sometimes 50, even 100 dog heads. Snakes writhed along its body, sometimes in manes around its heads. Some authors even described it with a dragon tail.

Who Was Cerberus?

Cerberus was a functional dog, fulfilling its purpose as the gatekeeper of Hades. Though it elicited horror in people, it was not necessarily a purely evil creature, says Peter Meineck, who is an associate professor of classics in the modern world at New York University.

Cerberus in Hesiod’s Theogony

The story of Cerberus dates back many millennia, to the ages of poets like Homer and Hesiod in the 8th and 7th centuries B.C. Hesiod coined the first overt, named reference to Cerberus in his poem Theogony, which chronicled the origins of the cosmos and the Greek pantheon.

Hesiod’s poem wasn’t put into written form until much later, since Greek culture was a heavily visual and oral tradition. One reason why descriptions of Cerberus flicker over time can be attributed to the human imprint left by the storytellers who spent generations passing down myths.

The Origins of the Cerberus Dog

Mythmaking was not a solitary process. Hesiod’s Theogony has nearly exact parallels with Sumerian and Babylonian creation stories, according to Meineck. Vedic Indian stories similarly tell of dogs of death. Greek religious cults like the Eleusinian Mysteries, which focused on gaining a better afterlife, drew their influences from regions in ancient Africa like Nubia and Egypt.

As stories passed between cultures through trade, Greece’s location in the Mediterranean also made it a central hub for these cultural exchanges.

“The idea of the kind of creature that inhabits entrances to sacred places is something that we find in lots and lots of world mythology,” Meineck says. “I don’t think [Cerberus] is necessarily just a Greek story. I think it’s quite universal.”

Learn more about various other mythical creatures:

Cerberus and Greek Mythology

By far the most famous legend involving Cerberus centers around the famously admired Greek demigod, Heracles.

Cerberus vs. Hercules

Specifically, Heracles had the impossible task to overpower Hades’ hellhound without weapons as his final labor – 12 acts of penance for killing his family in a craze.

With the additional help of getting initiated into the Eleusinian Mysteries, Heracles managed to do what few others had done before: going to the realm of the dead and returning. He brought Hades’ guard dog to the world above, and along the way Cerberus’ poisonous slobber sprayed the Earth, sowing the origin story for the lethal plant, aconite (also known as wolfsbane).

The Story of Cerberus and Heracles

The legend of Heracles and Cerberus is foremost a story about triumphing natural order, Meineck says.

“People were afraid of the idea of transcending the barrier between life and death. They feared not respecting that barrier,” he says. “At the same time, they also loved stories about Heracles, who was constantly obliterating those barriers and refusing to stay dead.”

Read More: The Lore and Legends Behind 3 Medieval Monsters

What Type of Dog Is Cerberus?

Dogs hold an ambiguous position in mythology, according to Marie-Claire Beaulieu, associate professor of classical studies at Tufts University. Canines are associated with Underworld divinities and therefore the afterlife, but plenty of ancient humans owned dogs as shepherds, guardians, or just loving companions – just like us.

Is the Mythical Dog Cerberus Evil?

The mythic monster Cerberus was so dreadful, Beaulieu says, because it turned familiar associations of a beloved companion on its head.

“People have a guard dog, and Fido is their companion or whatever,” she says. “But in the Underworld, which is like this nightmare reflection of the normal world, then the guard dog is this horrible creature.”

Is the Cerberus Dog Part Snake?

But one of the most crucial things to understand about Cerberus is that it’s not just a hound. There were also hissing snakes on its body and it had a serpentine nature. (In fact, there are multiple snake species named after Cerberus.) To Greeks, Beaulieu explains, snakes navigated tricky in-betweens, for their ability to slither under and above the ground.

Meineck adds that on top of their associations with the Underworld, snakes were further linked with female power. Earth was a goddess named Gaia, who therefore oversaw the realm beneath ground as well.

What Does Cerberus Mean?

In a way, Cerberus was not just the guard dog of Hades, but of Earth itself. Even its name – which some scholars derive from the Greek word “kreoboros” meaning “flesh-eating” – roots him to the Earth. Hellhounds aren’t the only consumers of flesh to exist, when we consider the natural cycle of decomposition.

A Flesh Eating Dog

“The notion is that the bodies of the dead sink into the Earth, and only the bones are left,” Beaulieu says. “So Cerberus, for these medieval commentators, becomes the eater of flesh, which is none other than the Earth.”

That’s why the legend of Heracles, who tramples these natural orders of Earth, is so mystifying and disturbing. Ancient Greece is long gone now, but Meineck suspects Cerberus still has a story to tell us now, as our current world continues to face environmental changes and threats.

“If you actually do capture the guard dog of the Underworld, what do you unleash when you do that?” Meineck asks. “Does a human go too far, sometimes, in thinking that they can actually upset the realm of the Earth Mother? I think there’s a sort of cautionary tale in lots of these myths.”

Read more: Robots and Artificial Intelligence Have Ancient Mythology Origins

What Does Cerberus Symbolize?

Meineck, who specializes in applying cognitive science and theory to antiquity, explains that the human mind tends to fill in the gaps of what we don’t (and can’t) know. Those gaps get plugged with fiction, religion, spirituality, and myths.

And at their core, myths are ways to probe at the most pressing issues of our existence: Where did everything begin and where does everything end?

“Myths love to ask you questions and to lay out some problems of existence,” Beaulieu says.

In Greek mythology particularly, death is a hound which haunts both its characters and storytellers. Cerberus’ story was one way to make sense of death’s inevitability. Meineck says that even the Ancient Greeks were probably aware that their mythology was, on some level, fictitious.

“The big question is, did they believe their mythology or did they not? I think they could hold both ideas at the same time,” he says. “I don’t think many Greeks thought that they would go to the Underworld and meet Cerberus, right? But I think they understood that it’s a metaphor for the fact that when you die, you are not coming back.”

Read more: Grave Goods Reveal Beliefs About the Afterlife