DNA analysis: Old teeth reveal what actually killed Napoleon's army

It was supposed to be Napoleon's greatest triumph, but it turned into a catastrophe in military history: In the summer of 1812, the French emperor marched into Russia with some 500,000 soldiers. But only a fraction returned. The Russians retreated, systematically burning the country, and ultimately leaving Napoleon to occupy a burnt-out Moscow. During the retreat to the Russian border camps in the autumn and winter of 1812/13, around 300,000 men died—not in battle, but from cold, hunger, and, above all, disease.

Typhus was long considered the primary cause of death. But a recent study in the journal Current Biology paints a much more complex picture of the mass extinction.

A French-Estonian research team led by the Pasteur Institute examined the teeth of 13 soldiers from a mass grave in Vilnius, Lithuania. Discovered in 2001, the burial site contained over 3,000 hastily buried bodies—many still wearing their boots, some frozen in their death positions. The scientists used modern DNA sequencing techniques to extract microbial DNA from the dental pulp. Traces of pathogens that can persist for millennia are deposited there during systemic infections.

Unlike previous studies that specifically searched for certain pathogens, the researchers sequenced the entire DNA and compared it with databases of all known microbes – an unbiased approach that was only made possible by modern technology.

The result was surprising: In four samples, the researchers found Salmonella enterica , the pathogen that causes paratyphoid fever, which is transmitted through contaminated water and food. In at least one sample, they discovered Borrelia recurrentis , which causes louse-borne relapsing fever. "We're talking about an army that was in a very fragile situation—a pathogen like that can really kill someone," study leader Nicolás Rascovan told the Washington Post .

"There's something perversely romantic about seeing typhus as the force that almost single-handedly destroyed Napoleon's army," historian Stephan Talty, author of a book on typhus in Napoleon's army, told the US newspaper. However, the new study shows that "other infections were at play"—hardly surprising given a huge army under "horrific conditions."

The researchers emphasize that their study by no means denies the role of typhus. It merely shows that other diseases were detectable in 13 of the more than 3,000 dead in this one mass grave. The excavation of the mass grave revealed the full extent of the catastrophe: horse skeletons lay next to human bodies, corpses had been hastily thrown into the ditch from the sides, others had been rolled over them. The skeletons suggested that the intense cold had frozen the victims in their death positions. The men were buried with their boots on—a sign that there was no time left for a dignified burial.

The new findings complement historical reports: In 1812, a military doctor named JRL de Kirckhoff described severe diarrhea, which he attributed to "large barrels of salted beets," the juice of which the soldiers drank out of thirst. However, the study now definitively presents evidence that Napoleon's defeat was not only militarily but primarily medically motivated—a fate that was probably inevitable in a time without antibiotics and modern hygiene.

RND/bab