Ancient DNA finally solves a 16th-century murder mystery

Two of Italy’s most powerful rulers died on back-to-back days in October 1587. They were not elderly, not ailing, and not at war. They died in a villa, less than a day apart, after suffering the same crushing fevers. Within hours of the second death, rumors had already named a killer.

Grand Duke Francesco I de’ Medici and his wife, Bianca Cappello, died within hours of each other after days of agony. At the time, the couple had shown symptoms of malaria, including a telltale intermittent fever. But rumors of an assassination immediately spread, pointing to Francesco’s younger brother and rival, Ferdinando, as the perpetrator. The accusation had logic behind it. Ferdinando was next in line to the throne, but he was at risk of being passed over in favor of Francesco’s illegitimate son, Antonio. Ferdinando had visited the grand duke and his wife at their residence just before they fell ill, further bolstering the suspicion that he poisoned them with arsenic to ensure his own rise to power.

For more than four centuries, the question of what actually killed Francesco de’ Medici was never fully settled. Historians debated it. Forensic scientists weighed in. A 2006 toxicological investigation even concluded the couple had been poisoned with arsenic. Now, in 2026, a team of researchers has done something none of their predecessors could: they pulled ancient DNA from 16th-century bones, sequenced it, and found the answer written in the parasite’s own genetic code.

The Ancient DNA Murder Mystery at the Heart of Renaissance Italy

The Medicis’ wealth and power did not insulate them from malaria. Many members of the Florence-based dynasty, which presided over Italian banking and trade from the 15th to 18th centuries, died from the illness. In 1562, Cardinal Giovanni de’ Medici, a scion of the dynastic family that dominated politics and banking in Tuscany during the Renaissance, died of malaria. Twenty-five years later, his older brother, Grand Duke Francesco de’ Medici, succumbed to the same disease. In a new study, Yale researchers in collaboration with paleopathologists from the University of Pisa in Italy conducted a genetic analysis of the brothers’ skeletal remains in search of several Plasmodium species, the parasitic protozoa that cause malaria.

The study, published in iScience in July 2026, represents the first time ancient DNA analysis has conclusively confirmed the cause of death for these two brothers. Valentina Giuffra, a full professor of history of medicine at the University of Pisa and co-author of the study, explained that prior attempts to solve the mystery used paleo-immunological analysis, which had pointed to malaria but could not be considered definitive. “The rumors would not stop, because paleo-immunology is not resolutive, and only ancient DNA could give an answer with a high degree of certainty,” she said.

Paleo-immunology uses antigens – substances that trigger an immune response – or proteins to check for traces of disease in ancient remains. DNA analysis, which is a more recent approach, is more definitive because it looks for direct genetic signatures of a disease.

What the Bones Revealed

To better understand how malaria impacted people in the region, including the Medicis, Giuffra and her colleagues turned to DNA from three of Francesco’s ribs and one of Giovanni’s. Both sets of remains are held in the Medici Chapels within the Basilica di San Lorenzo in Florence, where the brothers have been entombed for centuries.

What researchers found in Francesco’s bones was unambiguous. His remains carried detectable genetic material from two distinct species of the Plasmodium parasite – the single-celled organism that causes malaria and is transmitted through mosquito bites. Specifically, the iScience study recovered 185 base pairs of Plasmodium falciparum and 43 base pairs of Plasmodium malariae from Francesco’s rib samples. The symptoms described in 1587, including fever, chills, weakness, and declining health, are better explained by malaria than by arsenic poisoning.

Archival sources, including contemporary reports from court physicians, describe the symptoms the brothers suffered as consistent with malaria, which was called “febbre terzana” by residents of central Italy at the time. That phrase translates roughly to “third-day fever,” a reference to how malaria’s signature chills and high temperatures tend to cycle in recurring waves, typically every 48 to 72 hours. The reports also describe the treatments to which the stricken were subjected, including bloodletting, a common practice that likely did patients more harm than good.

The location mattered too. The couple fell ill in a Medici villa in Poggio a Caiano, near Florence, an area dotted with marshes and rice fields – ideal habitats for mosquitoes that can carry malaria. Anyone spending time in that environment in 16th-century Tuscany was at real risk of infection.

Giovanni’s Bones and a Previously Unknown Parasite Strain

The findings from Cardinal Giovanni’s remains were, in some ways, even more significant to science. Researchers not only confirmed that he died of malaria at age 19 in 1562 but also identified something no one had seen before: a previously unknown strain of Plasmodium falciparum carrying two unique genetic mutations.

The P. falciparum strain recovered from Giovanni de’ Medici includes two unique genetic mutations that likely derived from demographic expansion as the parasite spread across Europe, according to the study. This finding turns Giovanni’s bones into something more than a historical curiosity. They become a data point in understanding how malaria evolved and moved across a continent over centuries.

In 1562, Giovanni traveled to the Tuscan coast with his mother, Eleonora of Toledo, and his younger brother Garzia. Marshes in the area were full of mosquitoes carrying malaria. All three developed recurring fevers and died within a month. Giovanni was 19 years old.

As lead author Alexander Ochoa, an associate research scientist in Yale’s Department of Ecology and Evolutionary Biology and Department of Anthropology, explained: “The study of ancient DNA offers us an opportunity not only to diagnose malaria in the remains of individuals from the past, but it also offers us a window for understanding the evolution of malaria species, Plasmodium falciparum in this case, which can help scientists better understand how the pathogen adapts over time.”

The Science Behind Ancient DNA Analysis

Recovering usable genetic material from 16th-century bones is not straightforward. DNA degrades over time, and samples from Renaissance-era remains are fragmented and chemically damaged. The recovered DNA fragments were very short and showed the chemical changes expected in ancient genetic material. Those patterns support the conclusion that the DNA is authentic rather than the result of modern contamination.

Serena Tucci, assistant professor of anthropology in Yale’s Faculty of Arts and Sciences and senior author of the study, noted: “Our study is a great example of how we can use advanced ancient DNA laboratory methods to map the history of this deadly pathogen.”

The team was led by Yale University and the University of Pisa, with co-author Adalgisa Caccone, a senior research scientist in Yale’s Department of Ecology and Evolutionary Biology, emphasizing that the findings extend well beyond a cold case. “It also generated data that can inform current and future research on malaria, which remains a deadly disease that afflicts millions of people worldwide,” she said.

The study also analyzed nine other known ancient malaria-bearing samples from the same historical period, giving the researchers a broader picture of how the parasite circulated in Renaissance-era Italy. The finding that Francesco de’ Medici had traces of two malarial species aligns with earlier analyses of samples from Belgium from the same historical period showing co-occurrences of malaria in individuals. However, further genetic sequencing is needed to confirm that the two species were co-occurring in central Italy during the 16th century.

Malaria Then and Now

The disease that killed two of Tuscany’s most powerful rulers was so common in Renaissance Italy that court physicians had a local name for it. It didn’t register as unusual at the time – malaria was simply part of life in certain parts of the country. Valentina Giuffra noted that “malaria was one of the most widespread infectious diseases in Renaissance Italy,” and that it remained a major public health burden in Italy and other parts of southern continental Europe until the 20th century, when land reclamation projects and mosquito control finally led to its eradication.

The disease’s very name comes from an Italian phrase. Its name derives from the medieval Italian phrase “mal aria,” meaning bad air – a reflection of the pre-scientific belief that foul air rising from swamps caused the illness, rather than the mosquitoes that bred there.

Today, Plasmodium falciparum, the same parasite species found in both Medici brothers’ remains, remains the world’s deadliest malarial pathogen. According to the WHO’s malaria fact sheet, there were an estimated 282 million malaria cases and 610,000 deaths globally in 2024. Most of those deaths occur in sub-Saharan Africa, and the majority of victims are children under the age of five. The mosquito-borne disease that quietly felled a Renaissance grand duke is still one of the most dangerous infectious diseases on the planet.

Ferdinando: Off the Hook After 440 Years

The political context that fueled the poisoning rumors was real. The accusation focused on Francesco’s younger brother, Ferdinando I de’ Medici, as the most likely suspect. Rumors swirled that he had poisoned the couple’s food with arsenic, a preferred weapon of the Renaissance. No evidence of his guilt was produced at the time, but it was reasonable to think the deaths were political. Ferdinando opposed Bianca’s influence at court, and succession depended on Francesco’s death.

From the outset, Ferdinando de’ Medici’s behavior was suspicious and fueled rumors. He took charge of his brother’s illness, compiling medical bulletins and minimizing the gravity of his brother’s condition in dispatches to the Vatican. After the deaths, he ordered immediate autopsies – an unusual step, apparently taken to protect himself from future accusations.

The DNA evidence now exonerates him, at least in this case. Since 2004, when exhumation and analysis of skeletal remains began for 49 Medici family tombs as part of the Medici Project, various studies had confirmed malaria as the cause of Francesco’s demise. However, other studies published as recently as 2006 used toxicological investigations to determine that the couple were victims of arsenic poisoning. The 2026 ancient DNA study is the most definitive verdict yet – not because it simply confirms malaria symptoms, but because it finds the parasite’s own genetic fingerprint in the bone.

Read More: 7 of the World’s Oldest Diseases

What This Means for You

The resolution of this ancient DNA murder mystery does something beyond closing a cold case from 1587. It demonstrates that DNA can be recovered and interpreted from human remains that are more than four centuries old, with enough precision to identify not just a disease but a specific strain – and even novel mutations in that strain. That has direct implications for how scientists study pathogen evolution, track historical epidemics, and anticipate future ones.

For most readers, the practical takeaway is less about Renaissance Italy than about the disease itself. Plasmodium falciparum, the organism that killed Francesco de’ Medici and his younger brother Giovanni, is still the leading cause of malaria deaths globally. If you’re traveling to a malaria-endemic region, the CDC’s Yellow Book recommends prescription antimalarial medications such as atovaquone-proguanil, doxycycline, or mefloquine, depending on your destination – not herbal or homeopathic alternatives, and not the assumption that brief exposure carries no risk. The same parasite that thrived in Tuscan marshes in 1562 continues to adapt. The two unique mutations in Giovanni’s strain are a reminder that Plasmodium falciparum has been changing its genetic landscape for centuries – and it hasn’t stopped.

Disclaimer: This information is not intended to be a substitute for professional medical advice, diagnosis, or treatment and is for information only. Always seek the advice of your physician or another qualified health provider with any questions about your medical condition and/or current medication. Do not disregard professional medical advice or delay seeking advice or treatment because of something you have read here.

AI Disclaimer: This article was created with the assistance of AI tools and reviewed by a human editor.

Read More: Ancient Mystery of Iron Structures in the Australian Desert Finally Explained by Scientists

The post A 400-Year-Old Medici Murder Mystery Is Finally Solved by Ancient DNA appeared first on The Hearty Soul.