Caligula, the notoriously erratic Roman emperor known for his bloodthirsty cruelty, probably also possessed a nerd’s knowledge of medicinal plants, according to a new Yale study.

The study, by the Yale Ancient Pharmacology Program (YAPP), illuminates a brief anecdote about Caligula originally reported by the historian Suetonius in “The Twelve Caesars,” a second-century collection of biographies of Roman rulers from Julius Caesar to Domitian.

In the story, an unnamed Roman senator of praetorian rank who is suffering from an unspecified ailment takes a leave of absence to the Greek spa town of Antikyra in hopes that his health will benefit from treatments made from hellebore — a flowering plant purported to have medicinal properties. The senator, perhaps pressing his luck, asks Caligula to extend his leave. In response, the emperor has the hapless senator executed, quipping that “a bloodletting was necessary for one whom hellebore had not benefited in all that time.”

Yale scholars, combining ethnobotanical field data and a close reading of ancient texts, offer new understanding of the passage, providing context about Antikyra’s place in the Roman Empire and Caligula’s familiarity with pharmacology.

“Our work suggests that Antikyra functioned as a kind of Mayo Clinic of the Roman world — a place where affluent and influential Romans visited for medical treatments not widely available elsewhere,” said co-author Andrew Koh, who is YAPP’s principal investigator and a research scientist at the Yale Peabody Museum. “It also provides evidence that Caligula, while a tyrant, was more knowledgeable about medicine than has been previously understood.”

The study, published in the journal Proceedings of the European Academy of Sciences and Arts, was also co-authored by Trevor Luke, a YAPP faculty affiliate and associate professor of classics at Florida State University.

Medical tourism in the Roman world

Located on the Gulf of Corinth in the Phocis region of central Greece, Roman Antikyra was a modest port town famed for its association with unique hellebore treatments. In ancient times, hellebore was valued as a purgative, a treatment for epilepsy, and a cure for mental illness, the researchers said. Ancient texts describe two varieties of the plant: white hellebore used to treat afflictions of the head and black hellebore used to clear the bowels.

Examining historical uses of hellebore is difficult in part because ancient peoples, unbound by modern taxonomic classifications, used the term “hellebore” to reference various plants, the researchers said. They also note that ancient identifications of plant life evolved over time and geography, leading to discrepancies in plant names.

Further complicating matters, local naturalists in modern Greece use identifications that clearly reference plants that are different than those described in ancient sources. For example, the researchers said, an herbalist in modern-day Antikyra, which today is a small fishing village, identified “elleboro” as dwarf elderberry, which is an altogether different plant than hellebore as described in ancient texts.

It is unlikely that hellebore grew in sufficient quantities around ancient Antikyra to sustain large-scale production of herbal medicines, the researchers concluded. Today, the closest large stands of hellebore they discovered were located more than 2,500 feet above sea level on the southern slopes of Mount Helicon, located southeast of Antikyra. (The hellebore specimens they discovered clearly match depictions in ancient sources.)

While not an abundant source of the plant, Antikyra was renowned for the perceived efficacy of the special medicinal hellebore potions prepared there, which were used to treat melancholy, insanity, epilepsy, and gout. Some? Antikyran hellebore potions contained another plant, identified as sesamoides in ancient texts, a special ingredient that rendered the purgatives safer to consume, the researchers said, citing an Antikyran medicinal recipe described by Pliny.

By the early first century BCE, Romans had learned of Antikyra’s reputation as a source of especially beneficial hellebore potions through the immigration of Greek physicians to Rome and the lively trade in Greek books, the researchers said.

“It is remarkable that Antikyra is mentioned in the historical record since it was never an important cultural or economic destination,” Luke said. “It was known for hellebore treatments and little else. It’s an example of ancient medical tourism. Roman bigwigs traveled there for treatments the same way that the rich and powerful visit Rochester, Minnesota, to avail themselves of the latest medical techniques and therapies available at the Mayo Clinic.”

Luke and Koh believe the spa town held personal appeal to Caligula: They posit that he likely suffered from an affliction that Antikyran potions were believed to cure.

The researchers will now analyze the phytochemicals in specimens they recently collected from the Greek landscape to test their efficacy and biochemical interactions in relation to their ancient reputations, Koh said. The analytic approach, he said, combines textual evidence with scientific evidence to better understand history and glean lessons from the ancient past that are applicable for today.

“Closely collaborating with Trevor, a top historian of ancient Roman, provides a strong humanistic foundation for our science team to build its work upon,” Koh said. “In turn, YAPP’s scientific research offers historians a unique opportunity to understand long-studied ancient texts in fresh new ways.”

A more learned Caligula

Suetonius’ account of Caligula’s life differs from his biographies of other emperors in that it is split into two sections: The first describes Caligula’s background and rise to power, the second is devoted to his erratic, cruel, and deranged behavior.

While not seeking to rehabilitate Caligula’s reputation, the researchers show that he probably was a more learned man than one might infer from the monstrous deeds described by Suetonious. They cite the philosopher Philo of Alexandria’s portrayal of Caligula as an emperor endowed with impressive stores of practical knowledge, including a strong understanding of trade routes and seamanship. Philo, one of the emperor’s most prominent critics, also comments on how Caligula distorted Apollo’s art of medicine for malicious purposes, suggesting the emperor possessed detailed pharmacological knowledge, the researchers said.

They also cite several stories demonstrating that Caligula, who has a reputation as an enthusiastic poisoner, indeed possessed a deep knowledge of poisons and antidotes. They note that Caligula was convinced that his father, Germanicus, had succumbed to poisoning, which would have motivated him to study pharmacology if only out of paranoia about suffering a similar fate.

Caligula was familiar with hellebore remedies, Luke and Koh suggest, pointing out that he suffered from epilepsy, insanity, and insomnia — all ailments that ancient people believed the plant could alleviate. Suetonius’ anecdote suggests that Caligula also had a sense of how long it should’ve taken for hellebore to heal the senator.

Caligula’s reference to bloodletting when joking about the doomed senator suggests that he had read Celsus, whose medical treatise De Medicina was composed during the reign of Tiberius, Caligula’s predecessor, and prescribes bloodletting as an alternative to hellebore in treating epilepsy, the researchers explained.

“It’s possible that Suetonius is wrong, and that Caligula wasn’t ordering the man’s execution but simply prescribing an alternative treatment that he had read about or knew from his own experience,” Luke said. “We’re presenting a more complete and well-rounded version of Caligula as a ruler who was in tune with the medical wisdom of his day. He’s dismissed as a madman, perhaps rightly so, but we show he very likely knew something about hellebore and pharmacology in general.”