Technology & Medicine › Medieval
Black Death (bubonic plague)
1347–1351· Event· Germs, drugs & genetics
Well documentedSolid records, physical evidence or scientific consensus.
A plague pandemic that swept from Central Asia through the Middle East and Europe in 1347–1351, killing perhaps a third to half of Europeans.
See it on the Technology & Medicine map →How it works
The bacterium Yersinia pestis spread mainly through fleas carried by rats, and in its lung form directly between people. It reached Sicily on Genoese ships in October 1347 and crossed Europe within four years. Victims developed fever and swollen lymph nodes called buboes; most died within days. Estimates vary, but 25 to 50 million Europeans died, roughly 30 to 60 percent, along with millions in the Middle East and North Africa. Plague then returned every decade or two for centuries.
Why it mattered
Labor became scarce, so surviving peasants won higher wages and serfdom weakened in Western Europe. Towns created health boards and quarantine. Fear also fueled massacres of Jewish communities falsely blamed for the disease.
How we know
Chronicles such as Boccaccio's Decameron, tax and burial records, mass graves such as London's East Smithfield, and ancient DNA from victims that in 2011 confirmed Yersinia pestis as the cause.
Still unknown or debated
How fast rat fleas alone could spread it is debated; human fleas and lice may have helped. A 2022 DNA study traced its origin to Kyrgyzstan around 1338.
Inside this (1)
Connections (3)
▸Black Death (bubonic plague) led to QuarantineWell documented
The connection
After the Black Death, plague returned in new waves about every decade. Port cities trading with the eastern Mediterranean noticed that outbreaks followed arriving ships and travelers. In 1377 Ragusa ordered newcomers from infected areas to wait 30 days before entering; Venice and others copied and lengthened the rule.
When and how
Ragusa (Dubrovnik), on the Adriatic coast of today's Croatia, by decree of July 27, 1377, during a later plague wave; Venice built its first lazaretto in 1423.
How we know
Ragusa's decree survives and explicitly targets plague; later health board records across Italy describe quarantine as a plague defense.
Debates and open questions
How effective early quarantine was is debated, since rats and fleas could slip past it; isolation rules in Milan's territory in 1374 may also count as a first.
▸Black Death (bubonic plague) was finally explained by the Germ theory of diseaseMostly agreed
The connection
The Black Death killed perhaps a third to half of Europe's people, but it was blamed on bad air, the planets or divine anger. Germ theory supplied the answer: in 1894 Alexandre Yersin and Kitasato Shibasaburō identified the plague bacterium in Hong Kong, later shown to spread through rat fleas.
When and how
Hong Kong, June 1894: Yersin, of the Pasteur school, and Kitasato, trained under Koch; Paul-Louis Simond showed the flea link in 1898.
How sure are we?
From 2011, DNA of the plague bacterium, Yersinia pestis, was recovered from Black Death burial pits in London's East Smithfield, confirming the medieval cause.
Debates and open questions
How plague spread so fast is still debated: rat fleas, human fleas and lice, or person to person through the lungs.
▸Streptomycin and the cure for TB now cures the plague behind the Black Death (bubonic plague)Well documented
The connection
Plague is caused by the bacterium Yersinia pestis, and streptomycin, discovered in 1943 and first used against tuberculosis, also kills it. Since the late 1940s, prompt treatment with streptomycin or newer antibiotics has cut bubonic plague deaths from roughly half of cases to a small fraction.
When and how
Discovered by Albert Schatz in Selman Waksman's lab at Rutgers, New Jersey, in 1943; used against plague in India and elsewhere from the late 1940s.
How we know
Clinical studies from the 1940s onward and modern WHO and CDC data show its effectiveness; plague still occurs, notably in Madagascar and the Democratic Republic of the Congo.
Debates and open questions
Antibiotic-resistant plague strains have been found in Madagascar; how widely resistance could spread is a public health concern.