What Really Happened to Napoleon’s Army in 1812?

Cold and disease tore into Napoleon’s army in the retreat from Russia. DNA research tells us more about the pathogens soldiers encountered.

By Helen Petre

The loss of hundreds of thousands of French soldiers in the retreat of the Russian campaign in 1812 was the beginning of the end for Napoleon. After successfully conquering much of Europe, something went terribly wrong. What happened? Historians suggested the cold Russian winter, starvation, and typhus, but what really caused the deaths of all those formerly victorious soldiers? 

Researchers from the Institut Pasteur’s Microbial Paleogenomics Unit and the Laboratory of Biocultural Anthropology at Aix Marseille University investigated pathogens found in the teeth of 13 soldiers buried in a mass grave in Vilnius, Lithuania, along the path of Napoleon’s retreat from Moscow in the winter of 1812. They identified two unsuspected pathogens, Salmonella enterica and Borrelia recurrents. Both of these pathogens are responsible for symptoms similar to those described as afflicting the soldiers. And they are both potentially fatal when combined with cold, hunger, and exhaustion. 

The retreat from Russia in 1812

In June 1812, the French emperor, Napoleon I, invaded Russia in the famous Russian campaign, or Patriotic War of 1812. By this time nearly all of Europe was under Napoleon’s control, with the exception of Britain, which was also at war with America, in the War of 1812. Of all Europe, Russia alone resisted Napoleon’s efforts to cut off trade with Britain, so Napoleon ordered his army to attack Russia. That turned out to be a very bad idea. Napoleon was confident. He thought he was going to conquer the whole world. He was wealthy. He was married to Marie Louise, the daughter of the Emperor of Austria. He had gifted her an emerald and diamond necklace and matching earrings, which were stolen from the Louvre in October 2025. 

Napoleon’s army of 600,000 soldiers made it all the way to Moscow only to find the city destroyed and empty. The citizens had burned the crops and destroyed supplies and vanished. Winter was coming. Winters in Moscow are not mild. Knowing they would die of cold and starvation, the soldiers began their retreat in October 1812, thinking they could winter in Poland. It did not go well. Hundreds of thousands of French soldiers perished from cold, starvation, and disease along the way. This was the beginning of the end for Napoleon. What really happened? 

Was it typhus? 

It is not unusual for soldiers to die of disease. In fact three quarters of all soldiers who died in the American War of 1812 died of diseases, including typhus, typhoid fever, diarrhea, pneumonia, dysentery, small pox, measles, and malaria. Conditions of war are filthy. Soldiers slept in their uniforms huddled together, and shared lice-infected blankets. Medicine in 1812 was rudimentary. People were not even aware that disease was caused by bacteria, and there was no way to treat infections. 

J. Kirckhoff, a doctor serving Napoleon’s troops, authored a book detailing the illnesses that afflicted soldiers. He stated that soldiers suffered from typhus, jaundice, pneumonia, diarrhea, dysentery, and fevers. His conclusions agree with doctors from the American War of 1812. How accurate are these diagnoses? There were no tests, or ways to isolate bacteria to determine cause. Most of the diseases have similar symptoms and causes, such as lice and fecal contamination of food and water. 

Typhus was known as Camp Fever, and was generally accepted as the disease that caused the defeat of Napoleon’s Russian campaign. Typhus is caused by lice, and lice have been found in the remains of Napoleon’s soldiers who died in 1812 and were buried in mass graves along the route of retreat, in Vilnius, Lithuania. Lice is pretty common when humans live in close conditions and do not bathe. 

PCR identification of typhus in earlier studies

During a 2006 study, the bacterium responsible for typhus, Rickettsia prowazekii, and the bacterium that causes trench fever, Bartonella quintana, were detected in the teeth of Napoleon’s soldiers buried in the mass grave in Vilnius, Lithuania. Using the most innovative technology of the time, polymerase chain reaction amplification, the scientists could only copy short DNA strands. Results were prone to contamination and misidentification. Ancient DNA gets highly degraded and fragmented into pieces that are too small for PCR to work and can yield false positives. The study relied on only two short segments, 192 and 429 base pairs long. Molecular techniques have improved since 2006. 

Methods of current study of Napoleon’s army

Using the same soldiers, in the same grave, Rémi Barbieri and fellow researchers extracted dental pulp and sequenced DNA using a DNA sequencing machine. Dental pulp contains blood vessels, so the blood inside the tooth contains the same bacteria in the blood in the rest of the body. 

The scientists compared the sequences of DNA they extracted from the teeth, to known pathogen DNA sequences. The soldier’s DNA matched two bacteria: Salmonella enterica and Borrelia recurrentis, the cause of paratyphoid fever and relapsing fever, respectively. Both diseases result in high fever, fatigue, and digestive problems. 

The diseases found in DNA of Napoleon’s army

Paratyphoid fever

Paratyphoid fever is a serious disease that can be treated with antibiotics, specifically azithromycin, but is sometimes resistant. There were no antibiotics in 1812, nor did anyone think that disease is caused by bacteria. In fact, they had no idea what bacteria was. Symptoms of paratyphoid fever can last months if untreated. Some people carry the bacteria but have no symptoms. They are still able to transmit the disease to others. Paratyphoid fever is transmitted through contaminated water and food, not lice. It is common today in Asia, but not in developed countries. Infected individuals remain contagious for a year after symptoms resolve. 

Relapsing fever

Relapsing fever is transmitted by lice. Symptoms last five days, and then recur over time. Relapsing fever is currently prevalent in Sudan and Ethiopia. Antibiotics, such as tetracycline, are effective. Relapsing fever was described by the ancient Greeks. Or was it? Maybe it was trench fever they were describing? Who knows? The only way to accurately diagnose most diseases is to sample and grow the bacteria on a petri dish with media. We can now determine if a person carries a disease by DNA sequencing, but we cannot determine if the symptoms the person is experiencing are due to that disease, or even if the person has symptoms. 

Typhus

Typhus is the generally accepted, commonly suggested cause of death for soldiers, or any people clustered together in terrible conditions with lice and contaminated food and water. Up until now, everyone pretty much thought Napoleon’s army suffered from typhus while retreating from Russia in 1812. Since many diseases share symptoms, this common knowledge could be incorrect. Typhus causes high fever, fatigue, and digestive problems, like many other diseases. It is transmitted by lice and treated with antibiotics, specifically doxycycline. Some people still get typhus in the United States after exposure to infected flying squirrels. 

Trench fever

Trench fever was also documented in 2006 as a contributing disease to the demise of Napoleon’s army in 1812. It is transmitted by body lice and causes high fever, fatigue, and loss of appetite. Trench fever typically lasts five days and then recurs over time, with symptoms almost identical to relapsing fever. Trench fever is present today in the homeless population. Common antibiotics, specifically doxycycline, are effective. 

Updated disease-testing results 

Of the thousands of French soldiers buried in Lithuania, only 13 were used for sequencing. Of the 13, four were positive for S. enterica, the cause of paratyphoid fever. Two were positive for B. recurrentis, the cause of relapsing fever. Regardless of whether they died of cold or another cause, they died carrying evidence of these diseases. 

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Considerations

Thirteen is a very small sample, and only half of the 13 were positive for any disease. Using the newer technology, no soldiers were positive for typhus or trench fever. Considering that of the original 600,000 soldiers in Napoleon’s army around 300,000 died, and about 3,000 were buried in Lithuania, maybe we should consider what caused the deaths of the other 297,000? Of the 3,000 buried in Lithuania, only 13 were sampled. That is a very small sample. It is quite possible there is an error here. Also, it is really impossible to determine if disease was a major cause of soldier death, or if the soldiers actually died of starvation, cold, or exhaustion and just happened to be carrying or suffering from disease along with other hardships. 

It would be very, very helpful if the researchers had a comparison. Perhaps they could locate bodies of other citizens who also died in 1812 to determine if these bacteria were present in the general population. Sometimes bacteria are present at death, but not the cause of death. Sometimes disease strikes a general population regardless of state of war, weather, or lack of food. 

Even today, it would be impossible to distinguish between typhoid, typhus, and paratyphoid fever based on symptoms alone. 

Concluding takeaways 

High throughput sequencing of ancient DNA is a powerful approach to investigating historical disease and accurately identifying pathogens. This new technology allows us to question established conclusions and support new conclusions. It is reasonable to think that typhus and trench fever were the diseases that afflicted Napoleon’s men based on symptoms alone, but that does not mean this is an accurate conclusion. 

The results of this study reveal a correlation between the described symptoms and the bacteria present. It is possible that paratyphoid and relapsing fever were causes of some soldiers’ deaths, especially when combined with lack of food, freezing temperatures, and exhaustion in unsanitary conditions. 

We do not know for sure if the soldiers in Napoleon’s army died of paratyphoid fever and relapsing fever, but we do know that the bacteria that cause those diseases were in their bodies at the time of their deaths. The importance of this study and this technology is that we can now accurately determine which diseases were present at the time of death, instead of relying on commonly accepted conclusions based on symptoms alone. 

This study was published in the peer-reviewed journal Current Biology.

Reference

Barbieri, R., Fumey, J., Kabral, H., Scheib, C. L., Signoli, M., Costedoat, C., & Rascovan, N. (2025). Paratyphoid fever and relapsing fever in 1812 Napoleon’s devastated army. Current Biology, 35(21), 5384–5391.e4. https://doi.org/10.1016/j.cub.2025.09.047 

Featured image “Russian winter days” by sovraskin on Flickr, licensed as CC BY 2.0.