The Odyssey is fiction. But its monsters and magic may have been based on real science.

The Odyssey is a myth. It’s doubtful that a man took a literal decade to make it from Troy on the coast of modern-day Turkey to the Greek island of Ithaca after the Trojan War, cursed to make love to witches, journey to Hades, and pick fights with a cyclops. Or at least, if he did take that long, his curse probably involved not asking for directions.

But the tale of Odysseus’ extra-long journey home contains hints of things that people might have encountered in the ancient world, from a real-life cyclops to killer whirlpools and hallucinogenic plants. As Matt Damon steps into the famous wanderer’s sandals in The Odyssey on July 17, here are some of the scientific realities behind his legendary side quests.

(How do we know what ancient Greek warriors wore in battle?)

The cyclops

In the story, the cyclops Polyphemus—a giant with a taste for human flesh, and of course, only one eye in the center of his head—traps Odysseus’ crew and munches a few for lunch. Odysseus blinds Polyphemus with a heated spear, and the men make their escape, tied to the bellies of Polyphemus’ sheep.

One hypothesis for the origin of this mythical one-eyed giant lies in the fossils of Deinotherium giganteum, an elephant relative that roamed Europe, Asia and Africa between 23 and 8 million years ago. Paleontologists have unearthed its bones on the island of Crete, where the ancient Greeks could have come across them as well. Elephant skulls have relatively small eye holes, with a massive hole in the center. That hole is for the trunk. But as the elephants stood 15 feet (4.6 meters) tall at the shoulder, the huge skull might have been mistaken for the head of a huge, one-eyed person.

But the Greeks could also have been familiar with cyclopia, a rare and deadly congenital defect where the eye sockets and brain don’t properly divide as the human embryo develops. Instead of a nose, the fetus grows a tubular appendage, which usually appears above a single eye. Cyclopia occurs in only one out of every 100,000 human births. Sadly, 39 percent are stillborn, and those that survive birth do not survive longer than 13 hours.

While it is a very rare condition, scientists have estimated that at the time of The Odyssey, about 53 cases of human cyclopia would have been born around the world every year. In addition, other species can also exhibit cyclopia, including sheep, cattle and goats, especially if the mothers eat plants like hellebore.

The monster and the whirlpool

Odysseus made a clever escape from Polyphemus, but trapped between the six-headed sea monster Scylla and the mighty whirlpool Charybdis, he wasn’t so lucky. He loses his crew in a mighty storm, and morning finds Odysseus swept between the two. The dangerous passage has its basis in a real place—the Strait of Messina, a narrow channel that runs between Calabria in Italy and the island of Sicily.

In the strait, the Ionian Sea meets the Tyrrhenian Sea, and the two bodies of water have opposing tides—high tide in the Ionian is low tide in the Tyrrhenian, and vice versa, says Sergio Longhitano, a sedimentologist at the University of Basilicata in Italy, who published a 2018 paper on the strait’s tricky waters. So “in the center of the Messina Strait, there is a point that in oceanography is known as amphidromic point,” Longhitano says, where the height of the water never changes.

The height may not change, but the currents do, accelerating up to an estimated 5 meters per second (11 miles per hour) in strong winds or storms, Longhitano says. The fast, constantly switching currents and contrasting tides form strange water patterns. “Sometimes you can see currents diverging,” Longhitano says. Larger currents flow away from each other. Meanwhile, smaller currents are sucked in. When the sucked in currents flow in the same direction, “or when the two currents converge, you can have whirlpools,” he says. The tides in the region change every six hours, meaning there’s an opportunity for whirlpools in the strait multiple times per day. Charybdis is always lurking.

As for the six-headed monster Scylla, there is “this massive sea cliff that can be observed also from a distance, especially during the sunset. You can see a very dark shape stretching toward the northern part of the Messina Strait,” Longhitano explains.  Though it’s impossible to know Homer’s exact inspirations, he thinks it could be a good spot for a monster.

(Here’s what Homer’s Odyssey tells us about ancient Greek colonization.)

The lotus-eaters

Some of The Odyssey’s encounters entail far less peril, and seem more like drug-fueled parties. On one island, Odysseus sends scouts out to meet the inhabitants. But the inhabitants are “lotus eaters,” who share delicious “lotus” fruit that entrances the crew to desert their task.

Many people’s minds might immediately turn to addictive drugs like opium. But the ancient Greeks knew about poppies and opium, and they did not call them lotuses. Not only that, opium gets its own separate mention in the Odyssey, as “nepenthe,” a drug Helen of Troy mixes with wine to help the Greeks forget their troubles.

So what, then, was lotus? In a 2020 review, scientists were able to identify plants that the ancient Greeks referred to as “lotus” in seven different genera. A few are the water lilies we might describe as lotus plants today, in genus Nymphaea. But Homer says that the “lotus of the Lotophages” was a tree, and later writers, such as Herodotus, Theophrastus, and Pliny, place the lotus eaters in North Africa around the city of Tripoli in Libya.

“I don’t know of any ‘lotus’ that would cause memory loss,” says Joe Schwarcz, a chemist at McGill University in Montreal, Canada. “Some historians have guessed that the Greeks referred to the Chinese date tree as ‘lotus.’” Shrubby trees like the Chinese date are from genus Ziziphus. Plants in this genus produce a type of jujube fruit found in North Africa. It doesn’t have any psychoactive properties. But it can be fermented, and a dollop of alcohol is certainly good for forgetfulness.

(The Odyssey reveals a lot about the true history of the Bronze Age.)

The witch who turned men into pigs

On another island, the witch Circe waylays Odysseus and his crew with more memory issues; she blends them a potion with “potent drugs to make them totally forget their home.” When the men drink, they are turned into pigs. Odysseus goes to free them, aided by the god Hermes, who digs up a plant called Moly, with black roots and white flowers. Armed with the plant, Odysseus resists Circe’s magic and saves his men.

It would take real magic to turn men into pigs. But making men believe they are pigs is much easier, Schwarcz says. “The ancient Greeks certainly knew about plants that had mind-altering properties,” he says. Plants like datura (Datura stromonium), often called thornapple or jimsonweed, and belladonna (Atropa belladonna) contain compounds like atropine and scopolamine that block receptors for a chemical messenger in the brain called acetylcholine. “In the brain it is involved in memory formation and blocking its activity causes hallucinations and possibly delirium,” he says.

As for the “moly” that kept Odysseus safe, “the antidote to atropine poisoning is physostigmine which occurs in the Calabar bean,” (Physostigma venenosum), Schwarcz says. In a 2022 article, Schwarcz also suggests that Odysseus’ white flower could be snowdrop, Galanthus nivalis, which produces galantamine. Both of these chemicals block the enzyme that breaks down acetylcholine, which would increase the levels of the chemical messenger. (Diseases like Alzheimer’s are associated with reduced acetylcholine activity in the brain, and so galantamine and physostigmine have both been studied to treat it.)

The Odyssey makes it clear that plants can be medicine, but they can also be poison. “Perhaps the most misleading idea is that ‘natural is safe’ and that ‘nature knows best,’” Schwarcz says.

And while some of the encounters in the epic poem might have a basis in science, a little magic never hurt. Monsters can be made up, men can spin tales of the underworld and witches can concoct poisons. “It is just a story. And in a story, anything goes,” Schwarz says. “Plants can turn men into swine, although some people would argue that [plants] are not necessary for that transformation.”