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The Black Death and Justinian’s Plague: History’s Worst Pestilences

Khalid Elhassan January 8, 2025 13 min

Plague - Illustration from the medieval Liber Chronicarum 1, depicting skeletons rising for the dance of death — Illustration from the medieval Liber Chronicarum 1, depicting skeletons rising for the dance of death. Live Science

8. Weather and the Plague

The Yersinia pestis in the gut of an infected flea. Wikimedia

Fourteenth century weather fluctuations played a key role in the Black Death’s recurrences. The plague bacterium, Yersinia pestis, thrives on fleas that are usually hosted by ground rodents such as marmots – which don’t mingle with humans. However, bouts of bad weather in the 1300s struck those rodents’ habitats and decimated their populations. So their plague-infected fleas fled to alternate hosts such as rats – which do thrive amidst human populations. As seen below, a plague cycle developed, driven by weather fluctuations.

Written by

Khalid Elhassan

A lifelong history buff, I developed a particular passion for WW2 history as a child, when I spent hours listening to my grandfather, enraptured, as he recounted his wartime experiences in the British East African Campaign and with the British 8th Army in North Africa.

I graduated with a history BA from George Mason University, then went on to get a JD from the University of Virginia School of Law. After lawyering for a decade, I moved to sunny Rio de Janeiro and a less demanding career, opening a tourism agency in Copacabana.

A big chunk of my free time is spent blogging (you can follow me on Quora https://www.quora.com/profile/Khalid-Elhassan ) or freelance writing, mostly about my favorite subject, history.