The Black Death was one of the most devastating pandemics in human history, sweeping across Eurasia and North Africa in the mid-14th century. Arriving in Europe in 1347, it reshaped the continent’s demographic and social landscape in just a few years. The scale of mortality was unprecedented, with estimates suggesting it claimed the lives of 30% to 60% of Europe’s population. This event, also known as the Great Mortality, was a turning point in European history.
The Pathogen and Its Transmission
The Black Death was an infectious disease caused by the bacterium Yersinia pestis. This pathogen exists in a natural cycle involving rodents and their fleas. Transmission to humans occurred mainly through the bites of infected fleas from black rats, which were common on merchant ships and in urban centers. When an infected rat died, its fleas would seek new hosts, including humans, and transmit the bacteria.
Yersinia pestis caused three distinct forms of plague. The most common was bubonic plague, which develops after a flea bite and infects the lymphatic system. If the infection spreads to the bloodstream, it becomes septicemic plague. A third form, pneumonic plague, was the most virulent as it could spread directly from person to person through respiratory droplets when the infection reached the lungs. This person-to-person transmission allowed the disease to spread rapidly, independent of flea or rat vectors.
The Pandemic’s Journey Across Europe
The Black Death’s arrival in Europe is traced to the 1347 siege of the Genoese trading port of Caffa in Crimea. The besieging Mongol army was devastated by a plague outbreak. According to some accounts, the Mongols catapulted infected corpses into the city, though infected rats also likely crossed the lines. Fleeing Genoese traders then boarded ships, unwittingly carrying the disease across the Black Sea.
From these points of contact, the pandemic spread with speed along the continent’s trade routes. In October 1347, Genoese galleys arrived in Messina, Sicily, with dying crews. The plague quickly engulfed the island before moving to the Italian mainland and France. By mid-1348, it had established itself in Spain, Portugal, and England, reaching London by the winter.
The disease then moved eastward and northward, penetrating Germany, Scotland, and Scandinavia between 1348 and 1350. By 1351, the initial wave of the pandemic had swept through most of Europe.
Symptoms and Contemporary Explanations
The Black Death was marked by distinct and severe symptoms. For bubonic plague, individuals developed a sudden fever, chills, headaches, and weakness. The most characteristic sign was the appearance of buboes—painfully swollen lymph nodes in the groin, armpits, or neck. These could grow to the size of an orange and sometimes rupture. As the illness progressed, many suffered internal bleeding that resulted in dark patches on the skin, a symptom that may have contributed to the name “Black Death.”
Lacking an understanding of germ theory, medieval society struggled to explain the widespread death. The most prevalent medical theory was the miasma theory, which held that the disease was caused by “bad air” from rotting organic matter. To ward off the disease, people carried sweet-smelling herbs and burned incense to purify the air. Some physicians attributed the illness to an imbalance of the four bodily humors.
Many also interpreted the plague as divine punishment for humanity’s sins, fueling mass religious responses like public prayers. One extreme manifestation was the Flagellant movement, where penitents traveled between towns, publicly whipping themselves to atone for sins. In the widespread fear, minority groups, particularly Jewish communities, were scapegoated and falsely accused of poisoning wells, leading to violent persecutions.
Aftermath and Societal Reshaping
The Black Death’s massive demographic collapse, with a loss of 25 to 50 million people, created a severe labor shortage across Europe. With far fewer people to work the land, the value of labor skyrocketed. This shift in power greatly benefited the surviving peasantry.
The economic consequences were profound. Desperate for workers, landowners were forced to offer higher wages and better terms to attract tenants. This newfound bargaining power allowed many peasants to convert their labor services into cash rents, eroding the manorial system. As a result, the institution of serfdom went into a steep decline in Western Europe, largely disappearing by 1500.
The decline of the old feudal order paved the way for new social mobility, as peasants were no longer bound to their ancestral lands. While the immediate aftermath was disruptive, the 15th century became a period of increased prosperity for many survivors. They benefited from plentiful land and high wages, contributing to the gradual transition away from the medieval world.