7.7 — The Black Death

In 1348 the city of Florence lost, by the best estimates, somewhere between half and two-thirds of its people in a few months. Giovanni Boccaccio, who was there, wrote that the dead were so many that consecrated ground ran out, that huge trenches were dug and bodies stowed in them layer by layer "as merchandise is stowed in a ship", and that brother abandoned brother, and fathers and mothers refused to nurse their own children.

Between 1347 and 1351, somewhere between a third and half of Europe's population died. Comparable or worse mortality struck the Middle East and North Africa. In absolute terms it is probably the deadliest event, relative to the population alive, in recorded human history.

What the disease is

The bacterium is Yersinia pestis, confirmed by DNA recovered from the teeth of plague victims in mass graves in London, France and elsewhere. This settled a long argument about whether the Black Death was plague at all, and it was.

Its normal home is rodent populations, where it circulates without killing the host quickly. It reaches humans through fleas — the rat flea Xenopsylla cheopis especially — and the mechanism is unpleasant and important: the bacteria multiply in the flea's gut until they block it, so the flea cannot feed, becomes ravenous, bites repeatedly, and regurgitates infected blood into each wound.

Three forms, and they are very different.

Bubonic, the commonest: the bacteria travel to the lymph nodes, which swell into painful masses called buboes in the groin, armpit or neck. Untreated mortality around 50 to 60 percent.

Septicaemic: the bloodstream is infected directly. Untreated mortality near 100 percent, and it can kill within a day. Blackening of the extremities from clotting damage is where the name may come from — though "Black Death" is a later term, and contemporaries called it the great pestilence or simply the mortality.

Pneumonic: the lungs are infected, and this form transmits directly from person to person through coughing, with no flea required. Mortality is close to total without treatment. The pneumonic form is the reason the medieval outbreak spread so fast in winter and in cold northern cities where fleas are less active, and it is a substantial part of why the mortality was as high as it was.

Recent work has also raised the human flea and body louse as significant vectors, which would explain transmission patterns that rats alone fit poorly.

The spread

It came from Central Asia along the routes the Mongols had made safe (Chapter 7.6), reaching the Crimea by 1346 and Constantinople, Alexandria, Genoa and Venice in 1347.

The speed then followed the trade network exactly. Ports first, then rivers and roads inland. Sicily and southern Italy in 1347, France and Spain and North Africa in 1348, England and the Low Countries in 1348–49, Germany and Scandinavia in 1349–50, Russia in 1351.

And a few places escaped, which is itself informative. Milan enforced strict isolation of infected houses, walling them up with the occupants inside, and had far lower mortality. Poland was less affected, and the reasons argued include lower urban density and quarantine measures. Some isolated valleys and islands were untouched.

The word quarantine comes from this period. Venice and Ragusa required arriving ships to wait offshore before landing — thirty days, trentino, extended to forty, quaranta giorni. The forty was chosen for biblical resonance rather than epidemiology, and it happened to exceed the disease's incubation and course, so it worked.

What people thought was causing it

The medical consensus was miasma — corrupted air, produced by an unfavourable conjunction of planets. The Paris medical faculty produced a formal report in 1348 attributing it to a conjunction of Saturn, Jupiter and Mars in 1345.

Responses followed from the theory. Carrying flowers and herbs to counter bad smells. Lighting fires in the streets. Avoiding bathing, on the reasoning that hot water opened the pores to corrupt air — which was actively harmful.

Religious explanation was universal: divine punishment for sin. The flagellant movement — groups processing between towns whipping themselves in public penance — grew rapidly, and was condemned by the Pope in 1349, partly because it was outside clerical control and partly because it was fuelling massacres.

And the massacres are the part that must be stated plainly.

Jewish communities were accused of poisoning wells and were murdered across Europe — in Strasbourg in February 1349, several hundred to two thousand Jews were burned in the city's Jewish cemetery, before the plague had even reached the city. Comparable killings occurred at Basel, Mainz, Cologne, Erfurt and dozens of other places, and hundreds of communities were destroyed.

Pope Clement VI issued two bulls in 1348 stating that the accusation was false, pointing out that Jews were dying of the plague like everyone else, and threatening excommunication for those who attacked them. It had limited effect. In several cities the town authorities protected the Jewish community and were overruled by mobs or by guilds.

The demographic consequence is permanent: the destruction of Rhineland communities drove Jewish migration eastward into Poland and Lithuania, which is why the great Jewish populations of eastern Europe were where they were in 1939.

The consequences

This is what makes the Black Death a turning point rather than only a catastrophe.

Wages, land and the end of serfdom in the west

The mechanism is simple and it is one of the clearest cases of economics visible in the historical record.

Land was unchanged. Labour was cut by a third or more. So labour became scarce and land became abundant, and the price of each moved accordingly.

Real wages for labourers rose sharply — the English data show them roughly doubling over the following century, reaching levels not seen again until the nineteenth. Rents fell. Peasants could bargain, or leave for a lord who offered better terms.

Governments tried to stop it. The English Ordinance of Labourers in 1349 and Statute of Labourers in 1351 fixed wages at pre-plague levels and made it an offence to refuse work at those rates or to leave a manor. They failed, because a lord who needed his harvest brought in had every incentive to pay more quietly.

The resistance to enforcement fed the revolts. The English Peasants' Revolt of 1381, triggered by a poll tax, brought a large force to London; the rebels killed the Archbishop of Canterbury, and their demands included the abolition of serfdom. The revolt was suppressed and serfdom in England nonetheless dissolved over the following century, replaced by cash rents and wage labour.

And the geography split. In western Europe serfdom largely ended. In eastern Europe — Poland, Prussia, Hungary, Russia — landlords responded to the same labour shortage by tightening controls, and serfdom hardened, in some regions lasting until the nineteenth century. The historians' term is the second serfdom, and the divergence between western and eastern European labour institutions traces substantially to this response.

Why this matters for what comes later

Chapter 9.5 argues that the Industrial Revolution happened in Britain partly because British wages were unusually high relative to the cost of energy, which made labour-saving machinery worth building. The high-wage economy of northwestern Europe begins here.

That is a long causal chain and it should be held loosely. The link between fourteenth-century plague mortality and eighteenth-century machinery is argued by serious economic historians and it is not settled. The immediate effect on wages and on serfdom is not in doubt.

The Church

Clergy died at high rates because they attended the dying, and replacements were ordained hurriedly and poorly trained.

And the Church's inability to explain or stop the plague damaged its authority. Prayer, procession and penance did not work, and everyone could see that. Anticlericalism grew, lay religious movements spread, and the ground was prepared for the challenges of the following century — Wycliffe, Hus and eventually the Reformation (Chapter 8.7).

Medicine

Galenic medicine failed completely and visibly, which weakened the authority of ancient texts in a field where they had been unquestioned.

Practical public health emerged. Quarantine, boards of health in Italian cities, restrictions on burials and on assembly, and the beginnings of mortality statistics — the London Bills of Mortality, started in the sixteenth century for plague tracking, are the origin of vital statistics and eventually of epidemiology.

Art and mentality

The danse macabre — the dance of death, in which skeletons lead people of every rank away — appears in this period, and so does the memento mori tradition. The theme is equality in death, which is a specific response to a disease that killed bishops and beggars alike.

The other regions

The Middle East and Egypt suffered comparably — Cairo's population may have halved — and unlike Europe, several of those regions did not recover their population levels for centuries, in part because the plague recurred and in part because the political conditions after the Mongol destruction (Chapter 7.6) were worse.

And the consequences there ran the other way. Egypt's Mamluk state depended on tax revenue from a dense irrigated agriculture, and the labour loss broke the irrigation maintenance on which that agriculture depended. Where Europe's peasants gained bargaining power, Egypt's agricultural system contracted permanently.

China's population also fell substantially in the fourteenth century, though disentangling plague from the Mongol wars and the famines and the dynastic collapse is difficult, and whether the same disease reached China at the same time is debated.

It came back

The Black Death is the first wave, not the whole story. Plague returned repeatedly for the next three centuries — major European outbreaks roughly every ten to twenty years — which is why the population did not recover quickly.

The Great Plague of London in 1665–66 killed perhaps a quarter of the city.

And then it largely stopped in western Europe after the seventeenth century, for reasons still argued: better quarantine, the replacement of the black rat by the brown rat, changes in housing, or a change in the bacterium.

It has not gone away. Plague is endemic in rodent populations in the western United States, Madagascar, Peru, Congo and Central Asia, and there are a few thousand human cases a year worldwide. It is treatable with ordinary antibiotics if caught early, and it kills quickly if not.

Where this shows up in your life

Quarantine, public health boards, mortality statistics and the whole apparatus of epidemic response originate here.

The 2020 pandemic reproduced the pattern with uncanny precision: spread along trade and travel routes, initial denial, quarantine argued about, scapegoating of a minority, economic disruption, and labour market effects that persisted afterwards. Chapter 3.8 established that epidemics are the price of density and connection; this chapter is the largest single instalment of that bill.

And the economic lesson generalises. A shock that changes the ratio of labour to land or capital changes the bargaining power of everyone in the economy, regardless of what the law says. The Statute of Labourers is the standing example of a government legislating against a price change and being defeated by it, and Chapter 9.11 makes that a general point about prices.

What the next page covers

While Europe buried a third of its people, three empires in Africa were controlling the gold that European coinage was minted from, and one of their rulers made a pilgrimage that crashed the Egyptian gold market. Chapter 7.8 covers the empires of Africa — Ghana, Mali and Songhai and the trans-Saharan gold and salt trade; Timbuktu as a university city; Ethiopia's continuous Christian kingdom; Great Zimbabwe; the Swahili coast; and Benin — a set of states that most world histories omit entirely and that were, at the time, richer than most of Europe.