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


  • The 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.

Humans and epidemic disease

Epidemic diseases are those that spread through a large population in a short time. In order for an epidemic to occur, there needs to be a sufficiently concentrated population of humans interacting with one another.
Simply put, an epidemic is far more likely to happen in a city than in a sparsely populated region because in cities many people live and interact in a small area. People who contract a disease can be in contact with many other people and spread the germs before they even know they are sick. In contrast, a small community with little outside interaction is less likely to be exposed to contagious disease, and if it is, the disease is less likely to spread.
The spread of disease and trade went hand in hand, and no event illustrates this relationship better than the outbreak of bubonic plague in the mid-14th century, an event more commonly known today as the Black Death.
What is the relationship between urbanization and epidemic disease?

Origins of the plague outbreak

The bacterium yersinia pestis 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, and also carry fleas, making them an ideal vehicle - from the perspective of the plague, at least - for spreading the bubonic strain of the disease.
The bubonic form attacks the lymphatic system, which filters toxins from the body, leading to swelling of infected lymph nodes. The swollen nodes are called buboes, giving this form of the plague its name. But plague can take several forms. If a person develops pneumonic plague, which affects the lungs, they can spread it directly to other humans without the aid of infected fleas.
The plague caused an epidemic in China in the 1330s, and again in the 1350s, causing tens of millions of deaths. The same 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, providing 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?

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.start superscript, 2, end superscript
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. Europe had a smaller population than China, for example, so 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, too.
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. Taken as a generic analysis, this statistic can be slightly misleading, because oftentimes cities were harder hit than rural areas, seeing mortality rates of up to 80%, while rural areas with low population densities and little interaction with outsiders might not see any cases of plague at all.
Whatever the actual numbers, the massive loss of population - both human and animal - had major economic consequences. Cities 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: first, serfdom began to disappear as peasants had better opportunities to sell their labor.
Second, 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. Furthermore, high labor costs also caused governments to impose price controls on wages, but these efforts were often unsuccessful and sometimes met with rebellion.
Finally, the fear and confusion wrought by the plague sometimes led to violence, in part because of a lack of medical knowledge regarding how the plague spread. Jews, Romani, lepers, 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 what concerns us is 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.
As you have seen previously, 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.
  1. William J. Bernstein, A Splendid Exchange: How Trade Shaped the World (New York: Atlantic Monthly Press, 2008), 140.
  2. Bernstein, 140-141.