Black Death and the three plague pandemics: history, deaths and what changed

What the Black Death was

The Black Death was one of the deadliest pandemics in human history. It struck Europe between 1347 and 1351, killing a huge share of the population within a few years and transforming the economy, religion and society of medieval Europe.

The name “black” comes from the dark spots some patients developed, caused by bleeding into the skin. Today we know the disease was caused by the bacterium Yersinia pestis — the same one that causes plague today — and not by a virus or by “miasmas”.

When it happened

The Black Death is dated mainly to 1347 to 1351, with recurring outbreaks in the following decades. It is considered the start of the so-called Second Plague Pandemic.

Studies published in 2022 suggested the lineage may have originated in Central Asia, in the Lake Issyk-Kul region (present-day Kyrgyzstan), around 1338 — from where it spread along trade routes, including the Silk Road and maritime trade.

How many people died

Estimates vary widely, because medieval records are incomplete. The most cited figures for Europe range from 25 to 50 million deaths, equivalent to about 30% to 60% of the European population at the time.

Globally the numbers were even higher, though less precise. The Black Death is considered the deadliest pandemic in recorded history.

What caused it

For centuries the cause of the Black Death was debated. Confirmation came from genetics: in 2011, researchers extracted ancient DNA from victims buried in mass graves and identified Yersinia pestis, consolidating the bacterial explanation.

Transmission was mainly through rodent fleas, in a context of dense cities, intense trade and poor sanitation — an ideal environment for spread.

The three plague pandemics

Science groups the major historically documented outbreaks into three pandemics, separated by centuries — all caused by the same bacterium, Yersinia pestis.

Plague of Justinian (6th century)

The first recorded pandemic is named after the Byzantine emperor Justinian I, during whose reign the outbreaks hit the Byzantine Empire. It is thought to have begun in Egypt and spread across the Mediterranean, with the capital Constantinople among the worst-hit cities.

Death estimates vary widely, but run to tens of millions over two centuries, with recurring waves. The impact was so deep that historians debate its contribution to the economic and political decline of the period.

Third Pandemic (from 1855)

The Third Pandemic began in China, in Yunnan province, in 1855, and reached global scale through maritime trade. Hong Kong was a central hub in 1894 — it was there that the bacterium was identified that same year by Alexandre Yersin, whose name gave the genus Yersinia.

• It spread along maritime routes to India, Southeast Asia, and ports in Africa and the Americas.
• It caused more than 12 million deaths, mainly in India and China.
• It reached Brazil in 1899 through its ports, as described in Plague in Brazil.
• It was in this context that the role of the flea in transmission was established (Paul-Louis Simond, 1898).

Why a fourth pandemic is unlikely

The historical pandemics were catastrophic because there was no specific treatment, no understanding of transmission, and no surveillance. Today all three exist.

Does the Black Death still exist?

The disease never fully disappeared. Yersinia pestis still circulates in rodents and fleas in several parts of the world, and sporadic human cases are recorded every year — very differently from the historical pandemics.

What changed was not the bacterium but medicine: there are now effective antibiotics, rapid laboratory diagnosis and surveillance systems. That is why experts consider a repeat of the Black Death unlikely, even though cases and small outbreaks still occur. See also where plague exists today.