The Black Death and the Mongols: Biological Warfare at Caffa

If you’ve ever heard the claim that the Black Death was “launched” into Europe by the Mongols, chances are it led you to one name: Caffa (also spelled Kaffa), a fortified port on the Crimean coast of the Black Sea. In the mid-1300s, it was a busy trading hub controlled by Genoese merchants, connected by ship routes to the Mediterranean world. Spices, grain, cloth, and slaves moved through its harbor—along with sailors, caravans, and rumors. In 1346, that port became the center of a siege that later generations would remember not just as a military episode, but as a possible turning point in one of history’s deadliest pandemics.

Medieval port of Caffa (Kaffa) on the Black Sea with Genoese walls and ships.

According to the famous story, a force from the Golden Horde—often labeled “Mongols” in Western accounts—surrounded Caffa during a conflict tied to trade and regional power. Sieges were brutal, slow contests of endurance: defenders lived behind walls with limited food, cramped streets, and declining sanitation; attackers lived in camps where disease could move quickly through crowded ranks. In this tense setting, an outbreak struck the besieging army. Death spread through the camp, and fear spread even faster. This is where the story becomes unforgettable: some accounts claim the attackers hurled plague-infected corpses over the city walls, hoping to contaminate Caffa and break its resistance. That detail—horrifying, cinematic, and easy to repeat—has fueled debates for centuries.

But the most important part for understanding why this event matters isn’t just the image of bodies in the air. It’s what happened next. As the siege tightened and disease threatened both sides, ships left Caffa, carrying refugees, merchants, and crews to other ports across the Black Sea and onward to the Mediterranean. Medieval ports were perfectly designed for rapid spread: people packed into vessels, supplies were stored for weeks, and constant contact with new towns at every stop. Whether or not corpse-throwing truly “caused” Europe’s plague, the episode at Caffa captures the terrifying reality of the 14th century: war, trade, and disease were intertwined, and a single crisis at a crossroads could echo across continents.

In the sections ahead, we’ll separate what the sources actually report from what later retellings add—and explore what modern historians think about Caffa’s role in the Black Death’s westward surge.

Merchants vs. the Horde

To understand why Caffa became such a flashpoint in 1346, it helps to see it not as an isolated fortress, but as a high-value “gateway city.” Caffa sat on the Crimean coastline, facing the Black Sea—an area where steppe empires, coastal towns, and merchant networks collided. In the 1300s, the city was effectively a Genoese commercial colony: a fortified port used as a base for trade, banking, and shipping. Genoa wasn’t ruling Crimea like a modern nation-state, but it held strategic enclaves and negotiated (and sometimes fought) for the right to operate them. That meant walls, armed guards, warehouses, and the kind of wealth that attracted both partners and predators.

On the other side stood the Golden Horde, a powerful successor state of the Mongol Empire that dominated large parts of the Eurasian steppe. European sources often simplify the attackers as “Mongols” or “Tatars,” but the Golden Horde was a complex political force with its own elites, rivalries, and economic interests. By the mid-14th century, its leaders relied heavily on taxation and control of trade routes for revenue. A port like Caffa wasn’t just a distant outpost—it was a cash machine. It connected inland caravan routes to sea lanes, and whoever influenced the port could profit from tariffs, tributes, and access to goods moving between Asia, the Middle East, and Europe.

Genoese merchants trading goods in Caffa.

So why did tensions turn into a siege? The short answer is that trade brought wealth, and wealth brought conflict. Merchant colonies could flourish only as long as local powers tolerated them and benefited from them. When relationships soured—over taxation, political disputes, violence between communities, or shifting alliances—the same commerce that once created cooperation could suddenly become a reason to exert force. A siege was not only a military act; it was an economic strategy: pressure the city, disrupt its trade, and compel concessions.

It’s also important to picture what siege warfare looked like in this era, because it explains why disease could become a decisive factor. Caffa’s defenders were protected by walls, but walls didn’t create comfort. Inside, people crowded together—soldiers, merchants, craftsmen, families, servants, and refugees. Food supplies were finite, and the longer the siege dragged on, the more desperate conditions became. Water sources could be contaminated, waste could be piled up, and stress could weaken immunity. Meanwhile, outside the walls, the besieging army lived in camps that could be even more vulnerable: thousands of people and animals in close quarters, temporary sanitation, limited clean water, and constant movement of messengers and supplies.

That is why Caffa mattered so much—and why it was so dangerous. It was a place where global connections were concentrated in one point: ships in the harbor, caravans arriving, officials collecting dues, and soldiers trying to hold or break the city. In a world where armies and merchants traveled along the same routes, the siege created an environment where a local crisis could become a regional disaster—especially once ships began to leave the port.

The Corpse-Catapult Story

This is the question that pulls most readers into the Caffa story—and it’s also the point where history needs careful handling. The claim, repeated in countless articles and videos, is blunt: during the siege of 1346, the attackers supposedly threw plague-infected bodies over Caffa’s walls to spread disease inside the city. If true, it sounds like a medieval version of biological warfare. But what does “biological warfare” actually mean in a 14th-century context, and how likely is this event as it’s commonly described?

Medieval siege engine outside Caffa’s walls, representing the debated “biological warfare” claim.

First, it’s worth saying that using corpses in siege warfare wasn’t unheard of. Long before anyone understood bacteria or viruses, people still believed that rot, foul smells, and “corruption” could cause illness. Armies dumped dead animals into wells, polluted water supplies, and used decaying bodies to demoralize defenders. So the basic idea—using filth and death to pressure an enemy—fits the logic of medieval conflict. The crucial difference is this: a tactic can be “biological” in effect without being “biological warfare” in the modern sense. Medieval commanders did not have germ theory, did not isolate pathogens, and could not reliably control how a disease spread. If they used corpses, it was often based on an older understanding of contamination, not a scientific plan.

Second, we need to separate the three different possibilities that often get mixed:

1. Deliberate contamination: the attackers knowingly tried to spread sickness inside Caffa by throwing bodies.

2. Terror and psychological pressure: corpses were launched mainly to horrify defenders and break morale, with disease as a feared side effect.

3. Disease spread regardless: plague (or another epidemic illness) was already moving through camps and cities, and the siege simply intensified the conditions for it.

All three can produce the same outcome—panic, outbreaks, and flight—yet they imply very different levels of intent.

Another reason historians hesitate to treat this as an open-and-shut “first bioweapon” story is the nature of plague itself. Even if infected bodies were thrown into the city, plague transmission is not as simple as “corpse enters city → everyone gets sick.” The most widely accepted model involves fleas and rodents, and the dynamics of spread depend on what is present in the environment: grain stores, rats, crowded living quarters, and the constant movement of people and goods. A corpse might contribute to filthy conditions and fear, but it wouldn’t necessarily act like a guaranteed disease bomb. That matters because sensational versions of the story often imply a direct, immediate chain of infection that may not match how plague typically behaves.

So did it happen? The story is not pure fantasy—there is a well-known written account that describes something like this. But the safer historical approach is to treat it as a reported episode that raises questions rather than a perfectly documented fact. The real value of the “biological warfare” debate is that it forces us to ask: what did medieval people believe about disease, what tactics were normal in sieges, and how quickly could a crisis in a major port turn into a wider catastrophe once ships began to leave Caffa?

Myth or Evidence?

When modern historians discuss Caffa and the “corpse-catapult” story, they usually start with a simple problem: the evidence is famous, but not abundant. We don’t have a neat stack of military reports, city records, and eyewitness diaries that line up perfectly. Instead, we have a handful of medieval narratives, written in a world where chroniclers blended reportage, rumor, and moral interpretation. That doesn’t make the story useless—medieval sources are often all we have—but it does mean we have to weigh them carefully.

The account most often connected to the “plague bodies over the wall” claim comes from a 14th-century writer, Gabriele de’ Mussi, whose narrative describes disease in the besieging camp and the alleged use of corpses as a siege tactic. Historians debate how directly he was connected to the events and how much of his report was first-hand observation versus information circulating through merchant networks. In other words, his text may preserve a real memory of crisis at Caffa, but it may also reflect how people explained catastrophe in an age that lacked modern epidemiology. Chroniclers often looked for dramatic causes—punishment, corruption, villainy—because those frameworks made chaos feel readable.

Medieval manuscripts and a scribe’s desk.

That leads to the first major scholarly caution: Caffa is not the only doorway into Europe. The Black Death moved along multiple routes across Eurasia and the Mediterranean. Even if ships left Caffa carrying infected people, fleas, or rodents, that still wouldn’t automatically prove that Caffa was the single “source” of Europe’s outbreak. A pandemic is usually a network event, not a one-match wildfire. Ports, caravan towns, and regional hubs could each amplify spread in parallel.

The second caution is about mechanics. The traditional image—infected corpses launched into a city, instantly causing plague—sounds plausible at a storytelling level, but historians and scientists ask harder questions. What kind of plague was present? How would it transmit in that environment? Would the decisive factor be the corpses themselves, or the broader conditions of siege life—crowding, stress, poor sanitation, rodents, and constant movement? Many scholars treat the corpse-throwing episode as possible but not necessarily central. It might have been attempted as a terror tactic, or it may have happened in a more limited way than later retellings suggest.

So where does that leave us? A balanced historical conclusion looks like this: Caffa matters because it sits at a real crossroads—trade routes, shipping lanes, and human mobility. The siege likely did involve disease, and the city’s connections made it a plausible node in the westward spread. But the strongest version of the claim—“the Mongols invented biological warfare and directly caused the Black Death in Europe”—goes beyond what the evidence can firmly prove. Caffa is best understood not as a single origin point, but as a dramatic case study of how war and commerce could accelerate a catastrophe already moving through a connected medieval world.

From Port to Pandemic

If the Caffa siege matters as a potential link in the Black Death’s spread, it’s because it happened in the kind of place where diseases don’t just appear—they move. Medieval pandemics were powered by the same forces that powered prosperity: trade routes, ports, caravans, and the constant traffic of people and goods. Caffa was a hub where inland steppe networks met maritime highways. Once a major port like that was disrupted by war and sickness, the conditions for wider transmission were almost perfectly aligned.

The most widely accepted explanation for the Black Death’s rapid expansion involves Yersinia pestis, a bacterium that can circulate among rodents and be transmitted by fleas. In many outbreaks, fleas feeding on infected animals can jump to humans, especially when normal ecological balances are disturbed. Ports were especially vulnerable because ships carried more than people. They carried grain, cloth, barrels, ropes, and crates—the perfect habitat for rodents, along with the fleas that traveled on them. A ship could function like a sealed capsule of risk: cramped sleeping quarters, shared food stores, and limited cleanliness over days or weeks at sea.

Medieval ship departing a Black Sea port, illustrating how trade routes helped the Black Death spread.

Now, imagine the human side. A siege creates flight. When people fear starvation, violence, or disease, they try to leave. If ships departed Caffa during or after the crisis, they would have carried sailors, merchants, refugees, and soldiers, all in close contact. Even if only a small number were infected—or if infected fleas and rodents were aboard—the movement from port to port could amplify the danger. Maritime routes don’t behave like slow roads; they behave like fast channels. A vessel might travel from the Black Sea to Constantinople, then onward through the Aegean and into the Mediterranean, reaching bustling cities where crowds, markets, and dense housing made containment almost impossible.

But it’s crucial to understand why historians often say pandemics spread through networks, not single moments. Even if Caffa contributed, it likely did so as one node among several. Trade routes from the east had many branches, and by the time plague reached the Black Sea region, it may already have been circulating in multiple places. In that sense, Caffa is less a “starting gun” and more a “high-traffic intersection” where the impact could become visible and dramatic. War doesn’t need to create disease to accelerate it; it only needs to force people into unstable conditions and then move them along busy routes.

There’s also a quieter but powerful point: medieval people didn’t have to understand microbes for the system to work. They understood that something “bad” could travel with strangers, with cargo, with foul air, or with the dead. Their instinct to flee—often the most human response—could unintentionally help the disease leap from one community to another.

So when readers ask, “Did Caffa bring the Black Death to Europe?” the most careful answer is: Caffa could have been one of the bridges. Not the only one, not necessarily the first, but a plausible passage point where ships, trade goods, and human movement turned a regional crisis into a continent-wide disaster.

The Lesson of Caffa

The reason the Caffa story refuses to fade isn’t only because it’s dramatic—it’s because it feels like an explanation that ties chaos into a single, gripping cause. A siege. A sudden outbreak. A shocking tactic. Ships fleeing into the wider world. That sequence has the clean shape of a modern narrative, and readers naturally want a moment where the Black Death “began” for Europe. But history often doesn’t move like a movie. It moves like a web: multiple routes, overlapping crises, and causes that are easier to describe than to prove.

That tension—between a simple origin story and a messy reality—is exactly why the debate matters. When people label the Caffa episode “biological warfare,” they are using a modern term that carries modern assumptions: intention, control, and a clear understanding of how infection works. Medieval commanders didn’t think in those terms, but they did think about contamination and terror. They understood that filth could weaken an enemy, that dead bodies could demoralize defenders, and that fear could make a city surrender faster than arrows. So the question becomes less “Did they invent germ warfare?” and more “How did medieval people weaponize what they believed about sickness, corruption, and death?”

Medieval map and explorer's tools.

The story also matters because it reveals how pandemics and conflict feed each other. War creates crowding, scarcity, stress, displacement, and disruption of normal life—conditions that make outbreaks worse and responses weaker. Trade creates speed and connectivity. Put them together at a major port, and you get a perfect storm. In that sense, the most valuable lesson from Caffa isn’t a single act of corpse-throwing. It’s the broader reminder that systems spread disease: transportation networks, supply chains, migrations, and the fragile infrastructures of cities under pressure.

There’s another layer, too: the Caffa narrative shows how historical memory works. A chronicler’s account becomes a popular retelling. Popular retellings become certain. Certainty becomes a headline. And once a story is anchored to a vivid image—bodies flying over walls—it becomes hard to dislodge, even when historians add nuance. That doesn’t mean the story is false. It means the image is powerful enough to overshadow the careful questions: How reliable is the source? What else was happening in the region? What other routes carried the disease? What can we actually demonstrate?

In the end, Caffa remains compelling because it sits at the intersection of human choice and uncontrollable forces. People chose to besiege a city, to resist behind walls, to flee by ship, to keep trade moving. Nobody chose the plague. Yet those choices shaped how far and how fast catastrophe traveled. That’s why the episode still resonates today: it’s a medieval story, but it speaks to a modern truth—when societies are tightly connected, crises rarely stay local, and explanations that feel satisfying can still be only part of the picture.