Five thousand years ago, in what’s now southern Spain, a special set of women donned their ceremonial gowns, bedecked with tens of thousands of beads crafted from shell, ivory and amber. Perhaps before a crowd, pulsing to chants and drumbeats, these oracle-like figures hunched over a heap of radiant red powder. Then they inhaled the particles, or maybe downed them mixed in an elixir.

Ground from a mineral called cinnabar, the substance would have sent them into a fevered trance with tremors and delirium. On this mind-altering trip, the women may have liaised with deities and divined their society’s future—unaware that the powder’s potency came from its main elemental component: the toxic metal mercury.

As they repeated these rites throughout their lives, the poison built up in their bodily tissues. Millennia later, archaeologists measured mercury in the bones of these women and others from their community, revealing values orders of magnitude higher than what health experts consider tolerable today. It seems at this Copper Age site called Valencina, between about 2900 and 2650 B.C.E., ritual leaders intentionally ingested mercury-rich cinnabar for ceremonies or magic. More community members consumed it accidentally, while working with the pigment or through environmental contamination, according to a study published this past November in the Journal of Archaeological Method and Theory.

“These are enormous levels,” says Jerrold Leikin, a physician and toxic metals expert at the University of Illinois Chicago. He usually sees exposures presented as nanograms of mercury per gram of tissue, but the Valencina results report micrograms per gram—1,000 times as large. “One would expect significant symptoms,” says Leikin, who was not involved with the research but has collaborated with archaeologists to consider mercury in ancient humans from other regions.

As sufferers of acrodynia—the medical term for chronic mercury poisoning—the Valencina people might have their lost hair and developed rashes, Leikin says. They would have experienced memory lapses, fatigue and possible kidney failure. Both stillness and smooth movement would have been hampered by tremors, twitches and balance issues. And then anyone who inhaled powder or vapors with mercury may have suffered pneumonitis, or inflamed lungs.

“Western medicine has basically banned mercury … [like] public health enemy No. 1,” says Leonardo García Sanjuán, the study’s lead author and an archaeologist at the University of Seville in Spain. “But the truth is, the history of the relationship of humans with mercury has been quite complex.” The people of Valencina and other societies worldwide, spanning from at least 10,000 years ago to the present day, have used mercury-rich cinnabar for beauty, magic and traditional medicine—risk of debilitation or death be damned. The Valencina community’s newly measured, staggeringly high mercury values underscore just how socially or spiritually precious this blazing red rock was for some communities.

In volcanic regions, cinnabar forms from a union of mercury and sulfur when near-boiling fluids flow through rock cracks. “It creates this very vibrant color that doesn’t exist in other kinds of minerals,” says Vanderbilt University archaeologist Michelle Young. Nearly neon, the candy-apple red “has attracted people to the use of this toxic substance since very early time periods,” says Young, who studies cinnabar use in the ancient Andes but was not involved with the new study.

The mineral cinnabar forms in volcanic regions worldwide. H. Zell via Wikimedia Commons under CC By-SA 3.0

Past peoples ground and mixed cinnabar with an oil or egg yolk to make a paint. In places including Mexico, the Andes and Iberia, ancient inhabitants sprayed the pigment on graves and corpses, which rendered them stunning red and slowed the bodies’ decomposition. Roman Empire aristocrats adorned their walls with cinnabar-derived paint known as “Pompeian red.” European Renaissance artists called the rouge “vermilion” and used it to punch luminous red into grand portraits and religious scenes such as Titian’s Assumption of the Virgin.

But you won’t find cinnabar paint in Home Depot today. The mercury in it is toxic, and it is listed among the World Health Organization’s ten chemicals of public health concern. The metal can wreck the immune, digestive and nervous systems, and induce tremors, memory loss, headaches, partial blindness and more.

Symptoms depend on the amount, the duration of exposure and how the mercury is molecularly bound. For example, when pregnant people eat fish contaminated with the organic form, methylmercury, the toxin can harm their fetuses. In the 1700 and 1800s, milliners used a kind of mercury salt that inflicted irritability, depression and delirium, earning them reputations as “mad hatters.” The pure elemental form, a beady slate-colored liquid, can be fatal, but it commonly filled thermometers until 21st-century bans.

While scientists have primarily studied the mercury types in foods and industrial products, they understand relatively less about the health impacts of geologic forms like cinnabar. Cultures in the Caribbean, South Africa and Tibet still nibble or sniff cinnabar for its seemingly magical effects. And in traditional Chinese medicine, for centuries, healers have mixed cinnabar, herbs and animal parts to treat insomnia, heart palpitations, brain injuries and other ailments. About 40 of these recipes are still used today.

Recent testing of these drugs in living rodents or lab-grown human cells has shown that cinnabar chemically alleviates some symptoms, but too much will be harmful. One recent study, published in 2018, called for more research and careful monitoring of patients taking these substances, in order to safely balance the potential risks and benefits.

Cinnabar has landed people in hospitals—after accidental overdosing on traditional medicines, a suicide attempt or work in unsafe conditions with the substance. Turning to an ancient case, a study by Leikin and Yale University archaeologist Richard Burger concluded that although the Inca and other pre-Columbian societies of the Andes painted their bodies and belongings with cinnabar, such skin-deep exposure probably only had mild negative effects.

Crushing Cinnabar
In his Beijing studio, an artist grinds cinnabar to make paint. Li Xin / Xinhua via Getty Images

One past place where cinnabar figured prominently is Valencina. The site, twice the size of Disneyland, is about 20 minutes’ drive from Sevilla in southwest Spain. Twentieth-century archaeologists unearthed its ruins intermittently, but mostly during rescue operations related to construction. Over the last two decades, archaeologists have revisited the collections and excavations to make sense of the so-called mega-site.

Through this recent work, “the wealth of materials and the amazing archaeology of the site has been revealed,” says Marta Díaz-Guardamino, an archaeologist at Durham University in the United Kingdom, who has studied Valencina finds but was not involved with the new mercury analysis.

There, in the third millennium B.C.E., ancient Iberians constructed stone monuments, massive ditches, probable temples and graves. But archaeologists have not found permanent homes or ordinary village remnants. Valencina likely served as a sort of sanctuary, where people from across the region gathered for periodic ceremonies, deliberations and funerals.

One especially sumptuous tomb held an individual dubbed the Ivory Lady, who was buried between 2900 and 2800 B.C.E. with exotic items including an African elephant tusk and a clay platter bearing chemical traces of wine and cannabis. Another stone chamber built a century later harbored 20 dead, including the oracle-like women dressed in the ornate beaded garb and others with notably worn-down, arthritic vertebrae, shoulders and legs. The mostly female remains encircled what appears to have been a clay altar or stelae.

Both “are extremely exceptional graves in the context of the European Copper Age,” says Díaz-Guardamino. In addition to the rich goods, she says, “cinnabar powder is everywhere in those graves.” The super red, shiny powder blankets the bodies, artifacts and some interior surfaces.

In the mid-2010s, García Sanjuán teamed up with Steven Emslie—a University of North Carolina Wilmington paleontologist who usually probes chemical signatures in ancient and modern penguins—to test whether mercury also existed in the bones’ molecular structures. They suspected cinnabar snuck into the past Iberians while they were alive, in addition to covering the dead.

Emslie and University of Seville doctoral student Raquel Montero Artús measured mercury values in human remains from 23 Iberian sites used between about 6,300 and 1,600 years ago and published their findings in a series of studies between 2015 and 2022. The numbers from Valencina leaped out, orders of magnitude higher than mercury concentrations from most sites.

For the new study, published in November 2023, their team focused on Valencina and reported measurements for 70 humans and 22 animals. They found off-the-charts mercury exposure once again.

Comparing their findings to current health guidelines is tricky, because studies on living people often measure hair, which reflects substances ingested within weeks, whereas bone accumulates toxins over years. A person’s bones tend to concentrate less mercury than their hair. At Valencina, 65 percent of the measured humans had bone values that exceeded the U.S. Environmental Protection Agency’s safe threshold of 1 microgram of mercury per gram of hair. Several individuals surpassed values of 100, and two reached nearly 480. Even some animals measured in the double or triple digits. It’s “remarkable in terms of how widespread this mercury exposure appears to be,” says García Sanjuán.

The researchers think the variable levels suggest people with different roles ingested mercury in different ways. Those with relatively low counts—and the animals—likely consumed it accidently as cinnabar seeped into the soils and environment. Medium-level exposure may have afflicted workers and artists who used cinnabar to adorn beads, walls, burials and more. And the team suspects Valencina’s ritual specialists, most with counts exceeding 100 micrograms, swallowed or sniffed cinnabar to perform their magical duties.

Young finds this idea reasonable: “Ritual specialists would be most likely to want to use this kind of magic, prestigious pigment,” she says. “Any side effects of it, like tremors or strange behaviors, could seem to be related to their connection to the divine.”

She and others raised concerns, however, over whether mercury leached into the skeletons after the individuals died. “They have sprayed cinnabar all over the dead bodies,” says Kaare Lund Rasmussen, a chemist at the University of Southern Denmark who has studied mercury in medieval bones.

But the authors did not detect the highest values in the tombs with the most cinnabar, and some cinnabar-free graves had bones, nevertheless, loaded with mercury. To experimentally test the possibility of post-death contamination, the researchers have now buried fresh animal bones with cinnabar and will measure their elemental makeup in the future.

For whatever reason, Valencina’s cinnabar craze—and its regional prominence—faded after about 250 years. During its heyday, the site drew dispersed peoples to mix and mingle as they built monuments, celebrated special days and honored their dead. For Copper Age Iberians, central places like this “were very much the center of social life,” García Sanjuán says. “They were holding together the fabric of society.”

The Bronze Age followed, rife with social stratification, warrior elites and feuding states. “If you want to know what the Bronze Age is about, just read the Iliad,” says García Sanjuán. “It’s a bunch of really nasty, violent guys killing each other for the loot, for the plunder.” At least in Iberia, bygone were the sedate days of cinnabar-tripping oracles and communal sanctuaries.

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