DNA Settles 400-Year-Old Medici Murder Mystery: It Was Malaria, Not Poison

Ancient DNA extracted from 16th-century Medici remains confirms malaria killed Grand Duke Francesco I — resolving a centuries-old debate between poison and disease.

For over 400 years, historians debated whether Grand Duke Francesco I de' Medici and his wife Bianca Cappello were murdered by Francesco's power-hungry brother — or felled by disease. Now, ancient DNA analysis has delivered a verdict.

A new study published in iScience extracted genetic material from Francesco's skeletal remains and found clear traces of Plasmodium — the malaria parasite. Researchers from Yale University and the University of Pisa identified not one but two species of the parasite in his bones: Plasmodium falciparum and Plasmodium malariae, suggesting a double infection.

The circumstances were always suspicious. In October 1587, Francesco and Bianca died within hours of each other after days of agony at their villa in Poggio a Caiano, near Florence. The area's marshes and rice fields were notorious mosquito breeding grounds. But Francesco's younger brother Ferdinando had visited the couple just before they fell ill — and stood next in line for the throne.

Court physicians at the time documented symptoms consistent with malaria, including the telltale intermittent fever. Yet rumors of arsenic poisoning persisted for centuries, fueled by the Medici family's long history of intrigue and assassination. A 2006 study even claimed toxicological evidence supported the poison theory.

"The DNA is certain," said Valentina Giuffra, professor of history of medicine at the University of Pisa and study co-author. "It solves the problem and the doubts. I think this is a definitive answer." [CNN]

The team also analyzed remains of Cardinal Giovanni de' Medici, Francesco's younger brother who died 25 years earlier, and found a previously unknown strain of P. falciparum. The findings help fill a historical gap — Renaissance Italy is a period from which very little ancient pathogen DNA has been recovered.

Not everyone is convinced. Donatella Lippi of the University of Florence, who led the 2006 poison study, still maintains Francesco was poisoned, citing Vatican records of skin eruptions consistent with arsenic. The study authors acknowledge they cannot definitively rule out poisoning alongside malaria — but note the genetic evidence "decreases the margin for speculation."

Sources: CNN, iScience (PubMed)