The Black Death: Map of the Plague's Spread, 1346–1353

The pandemic began in the steppes of Central Asia, where plague circulates among marmots and other burrowing rodents. The earliest dated victims are buried in two Nestorian Christian cemeteries in the Chüy Valley near Lake Issyk-Kul in modern Kyrgyzstan, whose gravestones of 1338–1339 mention a pestilence; in 2022 researchers recovered the plague bacterium's DNA from their teeth and showed it was the ancestor of the strain that later struck Europe. Some historians still argue for a source nearer the Caspian Sea, but the Tian Shan region is now the most widely accepted starting point.

From there the disease travelled west with the caravans and armies of the Golden Horde, the Mongol state that ruled the steppe north of the Black and Caspian Seas. By 1346 it had reached the lower Volga, around the Horde's capital Sarai, and the Crimea. Turn the map to 1346 to see the Golden Horde at its height, with the Genoese and Venetian trading posts on its southern coast.

Caffa, today Feodosia in Crimea, was a Genoese colony and the busiest port of the Black Sea trade. Khan Jani Beg of the Golden Horde besieged it in 1343–1344 and again from 1345. According to the Italian lawyer Gabriele de' Mussi, whose account is the only one, the khan's plague-stricken army catapulted corpses over the walls. Historians doubt the story matters much: rats and fleas could cross siege lines unaided, and the plague was already moving along every trade route of the steppe.

What is certain is that ships leaving the Black Sea in 1347 carried the disease with them. Constantinople was struck in the summer of 1347 and Alexandria in the autumn. In October 1347 Genoese galleys put in at Messina in Sicily, and within weeks the plague had reached Marseille. Galleys from Caffa arrived in Genoa and Venice in January 1348, and Pisa followed a few weeks later, opening the way into northern Italy.

In 1348 the plague moved through Italy, southern France and Spain, reaching Florence in the spring, the papal court at Avignon early in the year, Barcelona in May and Paris by June. It landed in England at Melcombe, now part of Weymouth, in June 1348, reached London in the autumn and Ireland the same year. In 1349 it spread through the Holy Roman Empire, the Low Countries and Scandinavia, arriving in Norway on a ship that landed at Askøy, next to Bergen. Eastern Europe and the Baltic followed in 1350–1351, and the epidemic reached Novgorod in 1352 and Moscow in 1353.

Move the timeline from 1346 to 1353 to watch the dots spread: the plague advanced along sea lanes and rivers first, then inland at the pace of people and goods, a few kilometres a day. A few regions, among them parts of Poland and the Pyrenees, seem to have escaped lightly, though the records are thin.

The Islamic world suffered as badly as Europe. Plague reached Egypt in the autumn of 1347 and spread up the Nile and through the Levant in 1348, carried by ships, caravans and pilgrims. At its peak in Damascus, in September and October 1348, a thousand people were recorded dying every day. The pilgrimage brought it to Mecca in 1349. Historians estimate that about a third of the Middle East's population died, and Egypt, ruled by the Mamluk Sultanate, did not regain its pre-plague population for centuries.

Plague is caused by the bacterium Yersinia pestis, identified in 1894 and confirmed in the Black Death's victims by DNA taken from their skeletons. It usually passes to people through the bites of fleas that have fed on infected rats and other rodents. The commonest form, bubonic plague, causes fever and swollen, painful lymph nodes, the buboes, in the groin, armpits or neck, and killed perhaps half of those infected within a week. When the infection reached the lungs, pneumonic plague could pass directly from person to person through coughing, and it was almost always fatal.

Medieval doctors had no idea of germs. The medical faculty of the University of Paris blamed a conjunction of Saturn, Jupiter and Mars in 1345 and "corrupted air". People fled the cities if they could, burned aromatic herbs, and quarantined ships and travellers; the word quarantine comes from the forty days (quaranta giorni) that Venice and Ragusa later made ships wait.

No one counted the dead everywhere, so every total is an estimate. In 1351 agents of Pope Clement VI put the dead of Christian Europe at 23,840,000. Modern historians reckon that between a third and a half of Europe's population died in 1347–1351, and some, using manorial records, argue for as much as 60%: a total of roughly 25 to 50 million people. The worst-hit places lost up to 80% of their people; Florence fell from about 115,000 inhabitants in 1338 to about 50,000 in 1351, and Hamburg and Bremen lost at least 60%.

Across Eurasia and North Africa the death toll may have reached 75 to 200 million. China's population fell by at least 15% between 1340 and 1370, but how much of that was plague, rather than famine and the civil wars that ended Mongol rule, is unclear.

Looking for someone to blame, mobs turned on Jews, accusing them of poisoning wells. Pope Clement VI issued bulls in July and September 1348 condemning the accusations, pointing out that Jews were dying of the plague too, but the killings spread through Spain, southern France, Switzerland and the Rhineland. In Strasbourg about 2,000 Jews were burned on 14 February 1349, before the plague had even arrived. By 1351, 60 large and 150 smaller Jewish communities had been destroyed. Many survivors moved east into Poland, whose king Casimir III gave them protection.

Bands of flagellants marched from town to town whipping themselves in public penance, until the pope condemned the movement in 1349. Art turned to death: the Dance of Death and the Triumph of Death became common themes for two centuries, as the gallery below shows.

With so many dead, land was plentiful and workers were scarce. Labourers and tenants could demand higher wages and better terms, and lords and governments tried to stop them: England's Ordinance of Labourers of 1349 and Statute of Labourers of 1351 froze wages at their pre-plague level. The tension fed the revolts of the following decades, from the Jacquerie in France in 1358 to the English Peasants' Revolt of 1381. In western Europe serfdom withered; in the east, lords tightened it.

The plague did not go away. It returned in 1361 in the "pestis secunda", which struck children especially hard, and again roughly every decade, keeping populations low for a century. Europe did not regain its population of the 1340s until the 16th century. Outbreaks continued until the 18th century, among them the Great Plague of London in 1665–1666, which killed about 100,000 people, and Marseille in 1720.