The Black Death was a pandemic of bubonic plague — caused by the bacterium Yersinia pestis — that swept through Eurasia from the late 1340s onwards. It arrived in Europe via Sicily in 1347, carried on ships from the Black Sea, and spread with terrifying speed. By 1353, it had killed an estimated 30–60% of Europe's population — somewhere between 25 and 50 million people.
To understand the scale: imagine if between one third and more than half of everyone alive in the UK today died within five years. Not from war or famine, but from a disease that moved from village to village with no way to stop it.
Medieval people had no concept of bacteria or contagion — no germ theory, no understanding of how disease spread. When their neighbours began dying with swollen black lymph nodes, bleeding under the skin, and dark blotches (giving the plague its name), it seemed like the end of the world. Some thought it was divine punishment. Some fled the cities (often carrying the disease with them). Some blamed Jewish communities and carried out pogroms. The total incomprehension of the cause made organised response almost impossible.
How did it spread?
Bubonic plague spreads primarily via fleas on rats. The bacterium lives in the flea's gut; when a flea bites a human, it regurgitates the bacteria into the wound. In medieval Europe, rats were everywhere — in houses, food stores, ships. A pneumonic form (spread by breathing — person to person, far more deadly) also developed. Once pneumonic plague was spreading through a crowded medieval city, it was almost unstoppable.
What were the long-term effects?
Counterintuitively, the Black Death transformed Europe in ways that eventually improved life for survivors. With a third of the population dead, labour became scarce. Peasants who survived could demand better wages and conditions — the feudal system that had kept them in near-serfdom began to crack. It contributed to the end of medieval feudalism and the social upheaval that preceded the Renaissance. Some historians argue the labour shortages that followed accelerated the development of labour-saving technology.
The Black Death was a terrible disease that spread across Europe and Asia. It started in the late 1340s. The disease was caused by tiny germs called bacteria. Ships brought it to Europe through Sicily in 1347. The ships came from the Black Sea area. The disease spread very quickly and killed millions of people. By 1353, it had killed about 30 to 60% of all people in Europe. That means between 25 and 50 million people died.
To understand how many people died, think about this. Imagine if half of all your classmates disappeared from school forever. But instead of just your class, it happened to everyone in your town. Then it happened to half the people in the whole country. All this happened in just five years. It wasn't because of war or not having enough food. It was just one disease that moved from place to place. Nobody knew how to stop it.
People in medieval times didn't know about germs like we do today. They didn't understand how diseases spread from person to person. When their neighbours started dying with big black swellings on their bodies, they were very scared. The sick people got dark spots on their skin too. This is why it was called the Black Death. Some people thought God was angry with them. Some people ran away from cities to escape the disease. But often they took the germs with them. Some people even blamed other groups of people for the disease. Because nobody understood what caused it, they couldn't fight it properly.
How did it spread?
The plague spread mainly through fleas that lived on rats. The germs lived inside the fleas' stomachs. When a flea bit a person, it would spit the germs into the bite. In medieval times, rats were everywhere. They lived in people's houses, in places where food was stored, and on ships. There was also a type that spread through the air when people breathed. This type was much more deadly. Once this type started spreading in a crowded medieval city, it was almost impossible to stop.
What were the long-term effects?
Something surprising happened after the Black Death ended. Life actually got better for the people who survived. With so many people dead, there weren't enough workers left. The people who were still alive could ask for better pay and better treatment. Before the plague, poor people had to work for rich people and couldn't leave. This system started to break down. The Black Death helped end the old medieval way of life. It led to changes that helped create the Renaissance period. Some historians think the lack of workers made people invent better tools and machines.