What It Was and Where It Came From
The Black Death was a plague pandemic that swept Europe from 1346 to 1353, killing up to 50 million people. That amounted to somewhere between 30 and 60 percent of the European population and roughly a third of the population of the Middle East.
The cause is a bacterium, Yersinia pestis, spread mainly by flea bites and, in its lung form, by droplets between people. It normally lives in populations of fleas carried by ground rodents such as marmots across Central Asia and elsewhere.
The immediate origin is still argued over. A 2022 study pointed to two cemeteries in the Chuy Valley in modern Kyrgyzstan, where tombstones record a spike of deaths from pestilence in 1338 and 1339, and where the bacterium was recovered from victims' teeth. That strain was the direct ancestor of the one that reached Europe.
One suggested trigger is climate change in Asia, which pushed rodents off drying grasslands and into areas where people lived.
The name came much later. It was not called black at the time, and the English term is first recorded only in 1755.
Carried by Ships
The route into Europe ran through trade. Plague reached the Genoese trading port of Caffa in Crimea in 1347, and fleeing Genoese traders carried it across the Black Sea to Constantinople, where it arrived in the summer of that year.
From there it moved at the speed of shipping. Twelve galleys brought it to Sicily in October 1347. Ships reached Genoa and Venice in January 1348, and an outbreak in Pisa a few weeks later opened the way into northern Italy. One galley expelled from Italy arrived at Marseilles the same month.
Then it went overland. France, Spain, Portugal and England were struck by June 1348, then Germany, Scotland and Scandinavia between 1348 and 1350, reaching northern Russia in 1352 and Moscow in 1353.
Places outside the trade networks were largely spared, including much of the Basque Country and isolated Alpine villages. Once ashore, much of the spread appears to have been person to person as pneumonic plague, which explains why it moved inland faster than rat fleas alone could account for.
Forty Days
The word quarantine comes from this period, although isolating the sick was already an old idea.
The city-state of Ragusa, now Dubrovnik, introduced a thirty-day isolation period in 1377 for anyone arriving from a plague-affected area. It was later extended to forty days and took its name from the Italian word for forty, giving us quarantine.
Proving what had actually caused it took centuries. Alexandre Yersin identified the bacterium during an outbreak in Hong Kong in 1894 and suggested rats were the main vehicle. In 1898, Paul-Louis Simond worked out the mechanism: the bacteria multiply until they block a flea's gut, which starves the flea, drives it to feed aggressively, and causes it to flush thousands of bacteria into each bite.
The historical case was closed in 2010 and 2011, when researchers recovered the bacterium's DNA from teeth in plague-era mass graves across Europe and sequenced its genome from a London cemetery.
What It Left Behind
Europe's population did not return to its 14th century level until the 16th century, and the shortage of people reshaped the economy.
Wages rose sharply because labour had become scarce, and in some places rents collapsed, with properties that once brought in five pounds fetching one. Landowners had to substitute money rents for labour services simply to keep tenants on the land. Taxes became difficult to collect, partly because survivors refused to cover the share of the dead and partly because collectors would not travel to infected places.
The balance of power moved with it. Land was suddenly abundant, many survivors inherited property from relatives, and the value of ordinary workers rose, all of which helped destabilise feudalism. Workers began travelling to wherever conditions were best.
One argument holds that the devastation of Florence between 1348 and 1350 shifted how people thought and contributed to the Renaissance, though historians treat that as one factor among several rather than the explanation.
