In the summer of 1812, Napoleon Bonaparte led over half a million men into Russia, commanding what was then the largest military force Europe had ever seen.
His Grande Armée swept across Europe like a human tide, a symbol of Napoleon’s imperial ambition and absolute confidence. Yet, after six brutal months, only a few thousand soldiers would stagger out of Russia’s frozen wilderness in retreat.
Historians have long debated what truly destroyed Napoleon’s army, widely considered one of the most devastating military campaigns of all time. At the center of this debate lies the quest to identify the main cause for such overwhelming loss.
Shifting from the scale of devastation to the underlying causes, scholars have examined the reasons for the Grande Armée’s collapse. While some blamed starvation and frostbite, and others pointed to constant harassment by Russian forces, for more than a century, one explanation stood above all: typhus.
The louse-borne bacterial disease was infamous among armies of the 18th and 19th centuries, known for spreading rapidly through camps where soldiers slept in their uniforms and shared lice-infested blankets.
Now, more than 200 years later, a team of international researchers has rewritten that story, using genetic evidence extracted from the soldiers’ own teeth.
In a new study published October 24 in Current Biology, an international team of scientists revealed that Napoleon’s troops were likely struck down not by typhus, but by a combination of enteric fever and louse-borne relapsing fever—two infectious diseases that quietly ravaged the army from within.
“It’s very exciting to use a technology we have today to detect and diagnose something that was buried for 200 years,” lead author and professor at the Institut Pasteur, Dr. Nicolás Rascovan, said in a press release.
To carry out this research, the team examined dental remains from 13 French soldiers discovered in a mass grave near Vilnius, Lithuania, one of the final waypoints on Napoleon’s disastrous retreat from Moscow.
The burial site, first uncovered in 2001, contained thousands of skeletons interred hastily in frozen soil, some still wearing uniform buttons and regimental insignia. Historical records place the burials in late 1812, when the remnants of the Grande Armée collapsed amid starvation, disease, and relentless winter cold.
A new look at the remains of Napoleon’s Grande Armée
For years, earlier studies appeared to confirm that typhus was the culprit. In 2006, researchers detected Rickettsia prowazekii DNA using polymerase chain reaction (PCR) amplification.
However, while innovative at the time, that technology had limits. It could only copy short DNA strands, making results prone to contamination and misidentification in degraded samples.
Rascovan’s team used modern genomic techniques, applying advanced DNA sequencing to identify tiny ancient DNA fragments and match them to reference genomes. This approach, developed for paleogenomics, detects ancient pathogens even in heavily degraded samples.
“Ancient DNA gets highly degraded into pieces that are too small for PCR to work,” Dr. Rascovan explained. “Our method is able to cast a wider net and capture a greater range of DNA sources based on these very short ancient sequences.”
When the researchers sequenced the bacterial DNA from the soldiers’ teeth, each yielding about 20 million reads per sample, they found no trace of typhus. Instead, they identified two entirely different pathogens: Salmonella enterica Paratyphi C, the bacterium behind enteric (paratyphoid) fever, and Borrelia recurrentis, the louse-borne agent that causes relapsing fever.
Both diseases are highly debilitating. Enteric fever leads to high fever, severe diarrhea, weakness, and dehydration, all of which rapidly lower a soldier’s physical strength and immune defenses. Relapsing fever, transmitted by lice, causes recurring waves of fever and exhaustion, disrupting recovery and often leading to deterioration over several weeks. These effects severely hampered soldiers’ ability to march, fight, or recover.
Together, these illnesses could have crippled soldiers, whose bodies were already weakened by hunger and cold, as severe diarrhea, exhaustion, and high fever would have rapidly diminished their endurance and ability to survive the harsh conditions.
A grim picture emerges
Historical accounts align eerily well with the new findings. A French army doctor named J.R.L. de Kirckhoff, who served during the campaign, described widespread diarrhea and gastrointestinal distress among the troops as they reached Vilnius.
Kirckhoff noted that soldiers often consumed fermented beet juice from local barrels. “We encountered in almost every house, from Orcha to Wilna, large barrels of salted beets (buraki kwaszone), which we ate and drank the juice of when we were thirsty, greatly upsetting us and strongly irritating the intestinal tract,” he wrote.
That description fits the symptoms of enteric fever perfectly. “Diarrhea was common among us in Lithuania,” de Kirckhoff lamented, in a passage that modern epidemiologists now recognize as an unwitting observation of a foodborne epidemic.
Bringing together genetic evidence and historical accounts, this new study challenges previous understanding. It suggests that Napoleon’s army was not undone by a single sweeping disease, but by a toxic mix of overlapping infections—a convergence of microbial enemies that thrived amid misery and filth.
“A reasonable scenario for the deaths of these soldiers would be a combination of fatigue, cold, and several diseases, including paratyphoid fever and louse-borne relapsing fever,” researchers write.
The results also show how earlier conclusions about typhus may have stemmed from the technological limitations of their time. The 2006 PCR-based detections of Rickettsia prowazekii and Bartonella quintana (the bacterium that causes trench fever) relied on extremely short DNA fragments, which can yield false positives. However, using modern sequencing, Rascovan’s team found no reliable traces of either organism.
Beyond overturning previous assumptions, the study stands out for its method. The researchers authenticated even ultra-low-coverage DNA and identified Salmonella Paratyphi C, a human-specific pathogen that has been present since at least the Bronze Age.
Meanwhile, the Borrelia recurrentis strain told a deeper evolutionary story. It matched a lineage found in human remains from Iron Age Britain, suggesting that this strain of relapsing fever persisted in Europe for more than 2,000 years before eventually disappearing.
“This shows the power of ancient DNA technology to uncover the history of infectious diseases that we wouldn’t be able to reconstruct with modern samples,” Dr. Rascovan said.
Researchers mapped and authenticated every DNA fragment, using specialized tools to place pathogens into their evolutionary groups, even with limited data. Taken together, these findings paint a new portrait of Napoleon’s doomed invasion. By late 1812, after months of grueling marches, hunger, and bitter cold, soldiers were succumbing to infection even before the retreat began.
Contaminated food and poor sanitation would have accelerated the spread of enteric fever, while lice transmitted relapsing fever through exhausted ranks. Neither disease alone may have been uniformly fatal. However, together, they eroded the army’s strength from within, just as the Russian winter closed in.
“Even today, two centuries later, it would still be impossible to perform a differential diagnosis between typhus, typhoid, or paratyphoid fever based solely on the symptoms or the testimonies of survivors,” researchers write. “Our study thus provides the first direct evidence that paratyphoid fever contributed to the deaths of Napoleonic soldiers during their catastrophic retreat from Russia.”
Beyond its historical implications, the study is notable for underscoring the transformative impact of modern genomics on both archaeology and epidemiology. The ability to sequence ancient DNA now allows scientists to reconstruct the microbial landscapes of entire centuries—offering insights into how pathogens evolve, spread, and vanish over time. It’s the same technology that has traced medieval plague outbreaks, Viking smallpox, and even pre-Columbian leprosy across continents.
Building upon this, the Napoleon study adds another piece to that puzzle, showing how the movements of armies and the harsh logistics of war can serve as vectors for disease evolution. In this case, the emperor’s grandest campaign became a Petri dish of human suffering, accelerating infections that had haunted Europe for millennia.
For researchers, the work is as much about the present as it is about the past. Understanding how pathogens once spread through armies and populations can help scientists model how diseases may behave under future crises, especially in displaced or resource-deprived conditions.
“Our work demonstrates that high-throughput sequencing of aDNA is a powerful approach for investigating historical disease dynamics and underscores its capacity to accurately identify ancient pathogens, even when only limited genomic data are available,” researchers conclude.
More than two centuries after Napoleon’s Grande Armée froze and starved in the Russian snows, the truth of their suffering is finally coming to light. Ultimately, Napoleon’s greatest defeat wasn’t just a military one. It was biological.
Tim McMillan is a retired law enforcement executive, investigative reporter and co-founder of The Debrief. His writing typically focuses on defense, national security, the Intelligence Community and topics related to psychology. You can follow Tim on Twitter: @LtTimMcMillan. Tim can be reached by email: tim@thedebrief.org or through encrypted email: LtTimMcMillan@protonmail.com