The Mongols Helped Spread a Pandemic to Europe Through Biological Warfare

Ryan Fan
Photo of Jani Beg, the Khan of the Golden Horde. Public Domain

“If this account is correct, Caffa should be recognized as the site of the most spectacular incident of biological warfare ever,” Mark Wheelis, Emerging Infectious Diseases

As we continue to live through the COVID-19 pandemic, it’s crucial to look at past pandemics, and how they spread. In one case, in the spread of the plague to Europe in the 14th century, the Black Death spread in an utterly horrifying manner.

The World Health Organization says the bubonic plague killed an estimated 50 million people in the world in the 14th century. In Europe, a quarter of the population died from the plague.

Some historic accounts claim it all started when the Mongols besieged a city called Kaffa, a colony of the Republic of Genoa on the Crimean Peninsula. Today, it is the city of Feodosiya in Ukraine.

Outside the city walls, tragedy struck the Mongols. Heavy proportions of their army started dying because of the plague, which led the residents of Kaffa to think they were safe.

Gabriel de Mussis, an Italian notary, wrote a memoir of the siege, saying the Mongols started to hurl plague-infected cadavers over the walls of the city. This account is corroborated by the historian Varillas, and the hurling of the cadavers later led to the spreading of the plague to the residents of Kaffa. De Mussis claims those who fled the city brought the Black Death to the rest of Europe.

Mark Wheelis, a microbiologist at the University of California, Davis, finds the account plausible but contests the importance of the siege in spreading the disease to the rest of Europe. The plague spread west from the steppes of the Black and Caspian Seas. From Crimea, the plague spread to the rest of Europe.

This is the story of the Mongol siege of Kaffa, the subsequent spread of the Black Death, and the veracity behind de Mussis’s claims.

The history of Kaffa

According to Matthew Broughton at Montana State University, Kaffa was a city on the sea, and the citizens of the city had no navy at the time. As such, the Mongols had a hard time laying siege to the city.

Kaffa was a city made in an agreement between Genoa and the Golden Horde, the group of Mongols that settled in Russia. The Golden Horde was established by Batu Khan, the grandson of Genghis Khan. In the 1230s and early 1240s, on the verge of taking over Kievan Rus, Poland, Hungary, Austria, the Golden Horde was on the verge of taking over Europe, but the Mongols had to leave in 1241 following the death of the second son of Genghis Khan, Ogedei Khan. At the time, Batu Khan was in the process of besieging Vienna.

As for Kaffa, the city was set up as a port for Genoa and for trade with the Mongols. According to Wheelis, the Genoan traders and Mongols rarely got along — the Mongols were clearly in charge, and in 1307, the Khan of the Golden Horde, Toqtai Khan, arrested many Genoan residents because the Italians traded Turkic slaves. The Genoese burned down their city a year later as they fled.

The situation would only be ameliorated by the death of Toqtai, and the Genoese were welcomed back into the city. It started to thrive as a port city with two walls defending it from invaders: an inner wall that included 6,000 houses, and an outer wall that included 11,000 houses. The population was very diverse, including Italians, Greeks, Mongols, Turks, and Jews.

But the tension between the Mongols and the Genoese renewed in 1343, after a major brawl between Muslims and Italians in neighboring colony Tana. The Italian merchants fled to Kaffa, which greatly upset the Golden Horde. The new Khan of the Golden Horde, Jani Beg, laid siege to Kaffa to bring justice to the Italian merchants that year.

The siege failed — 15,000 Mongol soldiers were killed and Mongol siege machines were destroyed. Jani Beg tried to besiege the city again the next year, but this time, instead of the Genoese, the plague stopped his forces. Italians then took advantage of the suffering Mongols and forced them to allow the merchants to return to Tana.

De Mussis’s account of events

De Mussis was likely not actually in Kaffa during the events discussed, which damages his credibility. De Mussis is known to have been in the city of Placenza in 1347. His editor originally thought he was on a ship fleeing Kaffa, but now it is known that de Mussis was in Placenza during the whole epidemic. But he did have access to second-hand sources, and Wheelis sees his account as reliable as a result.

De Mussis starts his account by saying the plague was the punishment of the human race by God, who wants to punish the humans for their “limitless capacity for evil.” This condemnation against the sinfulness of humans goes on for a long time until he finally starts talking about the plague.

He says the plague came to Europe from the East, infecting “countless numbers of Tartars and Saracens.” This was a horrifying disease that brought sudden death to those it inflicted. By de Mussis’s accounts, thousands of Mongols died every day. The people of Kaffa expected the Mongols to lose interest in the siege as a result.

But the Mongols then ordered corpses to be put into catapults and thrown into the city, in hope that “the intolerable stench would kill everyone inside.” The residents of the city could not escape the infection of the rotting corpses, and they tried to throw the bodies into the sea.

The disease killed people instantly. And it was incredibly contagious, with de Mussis saying it could be spread “by look alone” (which isn’t true, but speaks to the swiftness and severity of the plague’s spread). Those who fled the city on boat then allegedly brought the disease to other “Christian areas” like Venice and Genoa, precipitating the Black Death’s carnage and devastation to the rest of Europe.


Since de Mussis is Italian and he refers to the Mongols as heathens, we can conclude he is a biased source. But Wheelis trusts de Mussis’s claim that the cadavers could have brought the plague into Kaffa. Those who disposed of cadavers had contact with infected material, which is a known method of transmission. This transmission was likely for those handling the cadavers since disposing victims’ bodies is usually a major cause of the outbreak.

But Wheelis pushes back against the notion that the Mongols threw the cadavers out of a desire to spite Kaffa — they may have not wanted to handle the dead bodies of those killed by plague themselves. Hurling those bodies into the city inevitably saved some Mongolian lives that would have been killed by the plague otherwise. The Mongols themselves abandoned the siege, leaving the city in Italian control, so biological warfare, in this case, was not meant for conquest.

As for the spread of the plague to the rest of Europe, Wheelis says it’s not like those who fled Kaffa did not spread the disease, but Kaffa was not the only Crimean port under Mongol control, and land trading routes probably spread the disease from Crimea to Europe as well.

Regardless, it remains frightening how disease can be used as a weapon. Whether biological warfare was used intentionally throughout history is unclear. Matthew Willis at JSTOR documents times in history smallpox was used as a biological weapon, although knowledge and intentionality of its transmission from colonists to Native Americans are unknown.

While the siege of Kaffa was not the only factor in the spread of the Black Death to Europe, it certainly played a factor. But it wasn’t as large of a factor as de Mussis documented.

Originally published on September 26, 2021 on Frame of Reference

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