If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content

Bubonic Plague

The plague, named the Black Death by later historians, had a devastating effect on the European population in the fourteenth century.


  • The diffusion of crops and pathogens, including epidemic diseases like the bubonic plague, often occured along trade routes.
  • The bubonic plague - named the Black Death by later historians - was caused by the yersinia pestis bacteria, which lived in rodent populations and was spread by fleas that had bitten infected animals.
  • Once the plague transferred to animals that were in close contact with humans and to humans themselves, it began to spread along established trade routes.
  • It is difficult to measure the exact human cost of the plague due to limited records from the historical period.
  • Most historians think that the plague killed somewhere between 30% and 60% of Europe’s population between 1347 and 1351.

Trade and disease

The spread of disease and trade went hand in hand, and no event illustrates this relationship better than the outbreak of
plague in the mid-14th century, an event more commonly known today as the Black Death.
In a passage from his book titled The Decameron, Florence, Italy resident Giovani Boccaccio described the Black Death, which reached Florence in 1348:
It first betrayed itself by the emergence of certain tumors in the groin or the armpits, some of which grew as large as a common apple, others as an egg, some more, some less . . .
From the two said parts of the body this deadly [bubo] soon began to propagate and spread itself in all directions indifferently; after which the form of the malady began to change, black spots or livid making their appearance in many cases on the arm or the thigh or elsewhere, now few and large, then minute and numerous.
Historians and
are confident that the Black Death originated in east-central Asia, which raises the question: How did the plague make it to Europe?
To understand how the plague spread, we need to understand how the disease was transmitted, along with the broader economic and political contexts that made its spread possible.

Origins of the plague outbreak

The bacterium that causes the bubonic plague is called yersinia pestis. It can survive in rodent populations and is spread to other mammals, including humans, through flea bites. The point of origin for the Black Death was most likely a population of marmots—small, prairie-dog like rodents—in Central Asia.
Marmots generally avoid contact with humans, but rats will readily come in contact with both marmot and human populations. Rats also carry fleas, making them an ideal vehicle—from the perspective of the plague, at least—for spreading the bubonic plague.
The plague caused an epidemic in China in the 1330s, and again in the 1350s, causing tens of millions of deaths. The 1330s outbreak also spread west across Central Asia via traders using the Silk Road.
Historian William McNeill argued that caravanserai - rest stops for traders - facilitated the spread of the disease as traders and their animals interacted in close quarters. That proximity provided new hosts for the disease, who then carried it to new locations, repeating the process of introducing and spreading the plague along overland trade routes.start superscript, 1, end superscript
Why might expanded trade have made disease more dangerous?
Caravanserai at Selim Pass in present-day Armenia, built in 1332.
Caravanserai at Selim Pass in present-day Armenia, built in 1332. Image credit: Wikimedia
Interior of caravanserai at Selim Pass.
Interior of caravanserai at Selim Pass. Notice how tight the quarters are. The closeness of people and animals staying at caravanserai such as this would have made them ideal spots for disease to spread. Image credit: Wikimedia

The plague spreads

By the 1300s, several Italian city-states had established trade relationships throughout the Mediterranean and Black Seas. The Genoese had a successful colony at the city of Kaffa on the Crimean Peninsula, which they held with the permission of the Mongol rulers of the region. In 1344, disagreements between the Genoese and the Mongols led to conflict.
Note how much of Europe was linked via trade routes. Compare the map below showing the spread of plague to the routes shown here to see how the plague spread north from the Mediterranean ports. Image credit: Wikimedia commons.
In 1346, the plague reached the Mongol soldiers who were besieging the city of Kaffa. Stories from the period tell us that the plague devastated the Mongol army, forcing it to give up the siege. Some of these stories also include a more gruesome detail: the Mongols catapulted the dead bodies of the soldiers who died of the plague into the city.
Whether the Mongols intended to spread the disease, and whether the story is even true, is not clear. What is clear is that some residents of Kaffa were infected with plague.squared
The plague continued to travel through Asia, eventually hitting major cities such as Baghdad and Constantinople. From there, it traveled to Alexandria in Egypt, Damascus in Syria, and down the Red Sea to Mecca. From there it almost certainly entered the Indian Ocean trade networks. The plague also traveled with Genoese merchants back to Italy, first to the port of Messina in 1347, and then north through Europe over the next several years.
The first cases of plague in Europe were spread by Genoese traders returning from Kaffa. Note that the earliest areas of plague were around Constantinople and in the islands of Sicily, Sardinia, and Corsica, and also the port of Marseille. All of these would have been stops for Genoese ships on their way from Crimea to Genoa. (Genoa is on the coast roughly between Marseille and Milan.) Image credit: Wikimedia.
Taking both maps together, does the spread of the plague through Europe seem to have any relationship with important trade routes?

Effects of the plague

Most in-depth studies of the Black Death focus on Europe, but this is a result of the available source material and what historians have chosen to study, rather than any major differences in its severity or impact between Europe and Asia.
After all, Europe had a smaller population than China. In terms of deaths, it is likely the plague did more damage in China. Given the large volume of trade in the Indian Ocean, it is not surprising to find accounts that hint at the plague spreading throughout the Middle East and South Asia at this time as well.
Although the lack of clear records makes it hard to be precise, historians generally estimate the Black Death killed between 30% and 60% of Europe’s population between 1347 and 1351. However, death rates varied from place to place. Some areas saw mortality of 80% or higher, while other places remained almost untouched by the disease.
Whatever the actual numbers, the massive loss of population - both human and animal - had major economic consequences. Those cities hit with the plague shrank, leading to a decrease in demand for goods and services and reduced productive capacity.
As laborers became more scarce, they were able to demand higher wages.
This had several major effects:
  1. Serfdom began to disappear as peasants had better opportunities to sell their labor.
  2. High labor costs caused landowners to look for more efficient and profitable ways to use their land and resources, such as increasing livestock production and payments of rent in money, rather than labor.
  3. High labor costs also caused governments to impose price controls on wages, but these efforts were often unsuccessful and sometimes met with rebellion.
  4. The fear and confusion caused by the plague sometimes led to violence, in part because of a lack of medical knowledge regarding how the plague spread. Jews,
    , and other religious and cultural minorities were sometimes blamed for causing or spreading the plague and became targets of attacks. It should be noted that the plague did not cause these social tensions, but rather created a context that made these tensions stronger and more likely to lead to violence.
How did the plague disrupt economic and social activity?
Why is it important to consider what medical knowledge of the plague people in the fourteenth century had when we try to understand their responses to it?


Although today we understand the medical aspects of the plague in ways that fourteenth century people could not, as historians we consider how the people who lived through it understood the plague and what impact it had on their actions.
From the broader perspective of world history, the real takeaway from the Black Death is how the vast, interconnected trading networks that existed at this time made the spread of a disease like plague possible in the first place, and how it dramatically altered the local communities it infected.
The expansion of trade brought many benefits, increasing access to material goods and technology, as well as spreading knowledge. However, the plague illustrates how increased cross-cultural contacts along denser trade networks increased the potential damage that could be caused by disease.
It was not a coincidence that the plague outbreak in the mid-fourteenth century did more damage than the outbreak in the mid-sixth century. Rather, the greater devastation occurred because the world of the mid-fourteenth century was more connected through trade.

Want to join the conversation?

  • aqualine ultimate style avatar for user LJMRoche
    Did dead bodies still hold the plague virus?
    (9 votes)
    Default Khan Academy avatar avatar for user
  • male robot johnny style avatar for user Zayed Tabish
    Does Black Death Still Exsist
    (1 vote)
    Default Khan Academy avatar avatar for user
  • leaf grey style avatar for user Timothy Scrivener
    Why are there more sources from Europe? The growth of printing and rising freedoms? An explosion of danse macabre artwork and texts?

    EDIT: Also if it's because there's more artwork, why wouldn't there be as much artwork elsewhere?
    (4 votes)
    Default Khan Academy avatar avatar for user
    • aqualine tree style avatar for user David Alexander
      Availability of sources (because of the languages in which they were set down) is part of the reason (It's entirely possible that the Mongol Archives are filled with source material, but few scholars can and do read it), the other part is, as pointed out in the essay, "... what historians have chosen to study, " Historians may be more interested in studying such things as pertain to Europe and the West, rather than to China and the east.
      (4 votes)
  • blobby green style avatar for user Rebecca DeVivo
    What was the population in Florence after the Black Death hit in 1348?
    (4 votes)
    Default Khan Academy avatar avatar for user
  • mr pink orange style avatar for user LOStewartA58
    Why didn't the plague ever spread to North and South America?
    (3 votes)
    Default Khan Academy avatar avatar for user
    • aqualine ultimate style avatar for user Safiyyah Salman
      Because Colombus still hadn't "discovered" America. Europeans only became aware of the Americas in the late 15th century, more than 100 years after the plague outbreak. As a result, no trading routes had been created between the Eastern hemisphere and the Western one - thus, no disease could be spread.
      (2 votes)
  • starky tree style avatar for user Zob Rombie
    Didn’t most believe that sickness was spread through scent, because I recall that early doctors at the time wore those masks that looked like bird heads almost, they had a large beak-like section over the nose that held herbs and spices as incense to mask the smell of the plague. Were those in use during this time period?
    (5 votes)
    Default Khan Academy avatar avatar for user
  • blobby green style avatar for user ADRIANT
    Did they ever come close to finding a cure?
    (3 votes)
    Default Khan Academy avatar avatar for user
  • leaf blue style avatar for user Olivia  Maxfield
    How long would it take to die after being infected with the plague? And how exactly did the plague spread from person to person? Was it more common for people to be infected with the plague by other humans who had the disease or rats and fleas that were infected?
    (3 votes)
    Default Khan Academy avatar avatar for user
    • starky tree style avatar for user Msans
      Back then when we didn't have medicine, the plague would of killed off a person in one day.

      And the Bubonic plague is mainly spread by infected fleas from small animals. It may also result from exposure to the body fluids from a dead plague-infected animal. In the bubonic form of plague, the bacteria enter through the skin through a flea bite and travel via the lymphatic vessels to a lymph node, causing it to swell.
      It also was spread around by coughs from the infected person who already have the illness
      (4 votes)
  • hopper cool style avatar for user Elijah William Bryant
    How can we compare this with covid, and learn from it?
    (2 votes)
    Default Khan Academy avatar avatar for user
    • aqualine tree style avatar for user David Alexander
      The plague spread by bacteria, not by a virus. So that's a contrast.
      Like the plague, it seems that Covid started in China.
      Both plague and Covid can be met with good public health practices.
      We need to learn about transmission (the plague can be traced along the silk road, Covid along international airline routes). We need to learn good public health practices. We need, above all else, to care for each other.
      (3 votes)
  • mr pants pink style avatar for user caroline
    What were common preventative measures in cities at the time?
    (2 votes)
    Default Khan Academy avatar avatar for user
    • aqualine tree style avatar for user David Alexander
      By the time of the 17th-century physicians had subscribed to miasma theory, which was the idea that contagion spread through foul-smelling air. Prior to this time, plague doctors wore a variety of protective suits but it wasn’t until 1619 that a “uniform” was invented by Charles de l’Orme, the chief physician to Louis XIII. (this is from the excellent article on plague doctors found at allthatisinteresting.com
      (3 votes)