Medieval Europe · 1347–1351

What Was the Black Death?

By the Aurelius editorial team · 3 min read · Updated 15 October 2026

Last time: Magna Carta tried to bind a king with law. By the 1340s Europe was crowded, its towns busy, its peasants hungry for land. Then the plague came.

In the summer of 1348, a Sienese chronicler broke off his record of the city's affairs to write something personal: “And I, Agnolo di Tura, called the Fat, buried my five children with my own hands.” Across Europe, between 1347 and 1351, millions of families shared his grief.

From Central Asia to Sicily

The disease was plague, caused by the bacterium Yersinia pestis. In 2022 geneticists recovered its DNA from people buried in 1338–39 near Lake Issyk-Kul, in modern Kyrgyzstan, whose gravestones mention death by “pestilence”. From the steppe it spread along trade routes to the Black Sea.

In 1346 it struck a Mongol army besieging Caffa, a Genoese trading port in Crimea. The lawyer Gabriele de' Mussis, who was not there, claimed the Mongols hurled infected corpses over the walls. Whether or not that happened, Italian galleys carried the disease west. In October 1347 it reached Messina in Sicily; by 1348 it was in Italy, France and England, and by 1351 it had swept most of Europe.

Swellings the size of an egg

In Florence, Giovanni Boccaccio described swellings in the groin or armpit that grew as large as an apple or an egg, followed by black or livid spots. These were buboes, the mark of bubonic plague, spread by fleas. When infection reached the lungs it became pneumonic plague, passed from person to person by coughing and almost always fatal.

For a century historians blamed black rats and their fleas. Some researchers now argue that human fleas and lice spread it faster than rats could; others disagree. DNA from 14th-century plague pits, including East Smithfield in London, has settled what the disease was, but not every detail of how it travelled.

Contemporaries had their own explanation. In 1348 the medical faculty of Paris blamed a conjunction of Saturn, Jupiter and Mars in 1345, which had corrupted the air.

How many died?

No one counted. Historians estimate deaths from tax lists, manor records and the registers of clergy, who died in large numbers because they tended the sick. A common estimate is that between a third and a half of Europe's population died in four years. The Norwegian historian Ole Benedictow argues for about 60 per cent, a figure many think too high.

The toll varied. A 2022 study of ancient pollen, which shows farmland turning back into forest, found sharp declines in some regions and little change in others. In Siena, work on a vast new cathedral stalled in 1348 and was never finished; its unfinished wall still stands.

Penance and scapegoats

Many saw the plague as God's punishment. In 1348–49 processions of flagellants walked from town to town, whipping themselves to atone for the world's sins, until Pope Clement VI condemned them in 1349.

Others looked for someone to blame. Jews were accused of poisoning wells, and confessions were extracted by torture. Clement VI issued bulls in 1348 pointing out that Jews were dying of plague too, but in the Rhineland and beyond, mobs and town councils destroyed whole communities, often before plague had even arrived. In Strasbourg, on 14 February 1349, the city's Jews were burned; chroniclers put the dead at around 2,000.

A world with fewer people

The survivors inherited a changed economy. With labour scarce, wages rose and land became cheap. England's rulers tried to freeze wages at pre-plague levels with the Ordinance of Labourers in 1349 and the Statute of Labourers in 1351. Resentment of such controls, and of a poll tax, fed the Peasants' Revolt of 1381.

In western Europe serfdom gradually withered; in parts of eastern Europe, lords later tightened their grip instead. Plague returned again and again for more than three hundred years, and Italian cities learned to fight it with health boards, isolation hospitals and quarantine.

In their own words

“Brother was forsaken by brother, nephew by uncle, brother by sister, and oftentimes husband by wife; nay, what is more, and scarcely to be believed, fathers and mothers were found to abandon their own children, untended, unvisited, to their fate, as if they had been strangers.”

Giovanni Boccaccio, The Decameron, Introduction to the First Day, c. 1349–1353

Translation by J. M. Rigg (1903). Boccaccio lived in Florence during the epidemic. His introduction frames a collection of fictional stories but is widely used as an eyewitness description; it also borrows from older literary accounts of plague.

Why it happened

• Plague spread from Central Asia along trade routes linking the steppe, the Black Sea and Italy.
• Ships and caravans carried infected fleas, rodents and people quickly between ports and towns.
• A crowded, often undernourished population had no immunity and no effective medicine.

What happened next

• Labour shortages raised wages and weakened serfdom in western Europe.
• Massacres destroyed many Jewish communities in the Rhineland and beyond.
• Italian cities pioneered public health boards and quarantine.
• Survivors such as Boccaccio and Petrarch shaped the culture of early Renaissance Florence.

Why it still matters

In July 1377 the city of Ragusa, now Dubrovnik in Croatia, ordered travellers from plague areas to spend thirty days in isolation before entering. Venice and other cities later extended the wait to forty days, quaranta giorni, which gave us the word “quarantine”. In 2020, governments facing Covid-19 reached for the same tool.

Connected stories

• Clovis and the Kingdoms After Rome: The same bacterium caused the Plague of Justinian from 541, which Gregory of Tours described in Merovingian Gaul.

Sources

• John Aberth, The Black Death, the Great Mortality of 1348–1350: A Brief History with Documents (2005)
• Ole J. Benedictow, The Black Death 1346–1353: The Complete History (2004)
• Rosemary Horrox (ed.), The Black Death (Manchester Medieval Sources, 1994)
• Giovanni Boccaccio, The Decameron, Introduction to the First Day, translated by J. M. Rigg (1903)

Images are credited under each picture. Paintings and photographs come from public collections via Wikimedia Commons; scenes with no surviving image are marked as illustrations.