The Black Death: The Plague That Reshaped Medieval Europe

In October 1347, a fleet of trading galleys put in at the Sicilian port of Messina. The sailors aboard were dying — or already dead — covered in strange black swellings, burning with fever, their bodies giving off a stench the horrified townspeople would never forget. The authorities ordered the ships back out to sea, but it was already far too late. Whatever the galleys carried had stepped ashore. Over the next four years it would sweep across Europe and kill, by the most widely accepted estimates, somewhere between a third and a half of the entire population. People at the time simply called it the Great Mortality. We call it the Black Death.

It is difficult, from a comfortable distance, to grasp the sheer scale of what happened. This was not a bad epidemic in the ordinary sense. It was the deadliest pandemic in recorded human history, a catastrophe so total that it broke apart the social, economic and religious fabric of the medieval world and remade it. Whole villages vanished. Cities lost half their people in a matter of months. And the people who lived through it did so with no idea what was killing them, or why.

Where it came from

The disease did not begin in Europe. It appears to have originated in Central Asia and spread westward along the trade routes that had recently knitted Eurasia together under Mongol rule — the same roads and sea lanes that carried silk and spices now carried death. One vivid and grimly famous episode comes from the Genoese trading post of Caffa, on the Black Sea, where a besieging Mongol army was struck by the plague. According to a contemporary account, the attackers catapulted their own infected dead over the walls into the city, in what is sometimes called one of history's earliest acts of biological warfare. Fleeing Genoese ships may then have carried the contagion onward into the Mediterranean, and so to Messina.

From Sicily it radiated outward with terrifying speed: into Italy and southern France in 1347–48, across Spain, up through France to England by the summer of 1348, into Germany and the Low Countries, and on to Scandinavia and beyond by 1351. Few corners of Europe were spared. In roughly four years a disease moving at the speed of medieval shipping and horseback had reached almost the entire continent.

The organism responsible

For centuries the precise identity of the Black Death was debated, but the strong scientific consensus today — supported by the recovery of ancient bacterial DNA from the teeth of plague victims in medieval graves — is that it was caused by the bacterium Yersinia pestis. This is the same microbe responsible for plague outbreaks into the modern era. It is normally a disease of rodents, spread by fleas, and it can infect humans in more than one form.

The bubonic form, the most common, produced the horrifying swellings — called buboes — in the lymph nodes of the groin, armpit and neck, often turning dark, which may be one source of the later name "Black Death." There was also a pneumonic form that settled in the lungs and could spread directly from person to person through coughing, and a septicaemic form that poisoned the blood. The pneumonic form in particular helps explain how the disease could rip through populations so fast and so lethally, especially in crowded, cold conditions. To medieval people, of course, none of this was knowable. They had no concept of bacteria, and their explanations ran instead to corrupted air, planetary alignments, and the wrath of God.

An eyewitness in Florence

One of the most powerful accounts we have comes from the Italian writer Giovanni Boccaccio, who lived through the plague in Florence and set the frame of his great story-collection, the Decameron, against it. His preface describes a society coming apart: the sick abandoned, the dead uncounted, social and family bonds dissolving in terror. It is one of the most unflinching descriptions of a disaster ever written.

Boccaccio describes how some people responded by shutting themselves away and living moderately, others by feasting and drinking through the terror on the logic that they might as well, and still others by simply fleeing the city and abandoning their homes, their goods, even their dying relatives. He recounts the grim sight of bodies piled at church doors and buried in mass trenches "like goods in the hold of a ship," layered with a little earth between them. The breakdown of basic human decency in the face of overwhelming death is the through-line of his account, and it is echoed in chronicles all across Europe.

Looking for someone to blame

A society that cannot understand a catastrophe will often look for someone to blame for it, and the Black Death produced some of the ugliest scapegoating in European history. As the plague spread, rumours took hold in parts of Germany and France that Jewish communities had caused it by poisoning wells. The accusation was baseless — Jews were dying of the plague alongside everyone else — but it triggered horrific waves of violence. In 1348 and 1349, Jewish communities were attacked and massacred in numerous towns, with entire populations burned or expelled, most infamously in Strasbourg in February 1349, where hundreds were killed before the plague had even fully arrived there. The Pope at the time, Clement VI, actually issued statements condemning the violence and pointing out that Jews were suffering and dying like everyone else, but the persecution raged on regardless.

Others turned the violence inward. Bands of flagellants — penitents who marched from town to town whipping themselves bloody in public — spread across Europe, convinced that only extreme self-punishment could persuade God to lift the scourge. The movement grew so large and so disorderly that the Church eventually moved to suppress it.

The myth of the plague doctor

It's a small correction, but a telling one — so much of our "medieval" imagery is actually early-modern, retrofitted onto the wrong century. The real medieval physicians of 1348 were largely helpless. Their best theories blamed "miasma," or bad air, and a corruption of the bodily humours; their treatments ran to bloodletting, herbal remedies, aromatic substances burned to purify the air, and prayer. None of it worked, because none of it addressed fleas, rats, or bacteria.

The world the survivors inherited

Here is where the story takes its most genuinely surprising turn. A catastrophe of this magnitude might be expected to leave only ruin behind, and in the short term it did. But for those who survived, the aftermath brought profound and in some ways improving change — and it flowed largely from one brutal fact: suddenly there were far fewer people, and labour became scarce.

Before the plague, Europe had been crowded, with abundant peasant labour that landlords could command cheaply. After it, with perhaps a third to a half of the workforce dead, surviving labourers were suddenly in demand. They could ask for higher wages and better terms, and they did. Landlords and rulers tried desperately to hold things in place — England's Statute of Labourers of 1351 attempted to freeze wages at their old levels and punish workers who demanded more — but the economic pressure was overwhelming. The bargaining power of ordinary working people rose, the old bonds of serfdom in Western Europe came under severe strain, and over the following generations they substantially weakened. Tensions of exactly this kind helped fuel uprisings like the English Peasants' Revolt of 1381.

The shaking of faith

The plague also struck at the spiritual confidence of medieval Europe. People had prayed, processed, flagellated themselves and begged God for mercy, and still the dying went on. The clergy were not spared — indeed, priests who tended the sick and gave last rites died in great numbers, and the gaps were sometimes filled by hastily ordained and poorly trained replacements. The Church's inability to halt the catastrophe, and the visible failure of its remedies, left a residue of disillusionment and questioning that some historians see as a long-term contributor to the religious upheavals of later centuries. At the very least, the easy confidence that the Church could mediate between humanity and disaster took a heavy blow.

Art and culture absorbed the trauma too. The decades after the plague saw a darkening of the European imagination — a new preoccupation with death, decay and judgement that surfaced in imagery like the danse macabre, the dance of death, in which skeletons lead away people of every rank, from pope to peasant. Death had paid a visit so total and so indiscriminate that European culture would not soon forget it.

The plague that never quite left

It is a common misconception that the Black Death was a single event that ended in 1351. In fact, the bacterium settled into Europe and returned in waves for the next three centuries. There were major recurrences in the 1360s and 1370s and repeatedly thereafter; the Great Plague of London in 1665–66 was one of the last severe European outbreaks. Each return reinforced the demographic depression and the sense that the disease was a permanent feature of life. Plague never entirely disappeared, either — Yersinia pestis still exists in rodent populations in parts of the world today, though it is now treatable with antibiotics and causes only a small number of cases each year.

What lingers most is the scale of the original blow and the strange double truth at its heart. The Black Death was an almost unimaginable human tragedy, the worst single mortality event humanity has recorded. And yet the depopulated, traumatised world it left behind was also one in which ordinary labour was suddenly worth more, old certainties were suddenly open to question, and the rigid structures of the medieval order had been cracked in ways that could not be fully repaired. The survivors did not see it as a new beginning — how could they, standing among the mass graves? But in the long, cold arithmetic of history, the catastrophe that emptied Europe also helped to remake it.

Image: citizens of Tournai burying the dead during the Black Death, from a fourteenth-century illuminated manuscript (public domain, via Wikimedia Commons).

Sources & further reading

• John Kelly, The Great Mortality: An Intimate History of the Black Death (HarperCollins, 2005).
• Ole J. Benedictow, The Black Death 1346-1353: The Complete History (Boydell Press, 2004).
• Giovanni Boccaccio, The Decameron (c. 1349-53; modern translations widely available, e.g. Penguin Classics) — the Introduction is a key eyewitness source.
• Rosemary Horrox (ed.), The Black Death (Manchester University Press, 1994) — a collection of translated contemporary documents.
• Encyclopaedia Britannica, "Black Death"; research on ancient Yersinia pestis DNA, e.g. Bos et al., Nature (2011).