History has a funny way of shrinking things down until they fit into a single textbook paragraph. If you ask most people when was the plague, they’ll immediately point to 1347. That’s the big one. The Black Death. The moment when ships from the Black Sea rolled into Messina, Sicily, carrying flea-ridden rats that would eventually wipe out nearly half of Europe’s population. But that’s just one chapter in a much longer, much deadlier story.
The plague wasn't a one-and-done event. It didn't just show up, kill a bunch of people, and vanish into the history books. Honestly, Yersinia pestis—the bacterium responsible for all this chaos—has been hanging around for thousands of years. It’s still here. If you go hiking in the American Southwest today and mess with a prairie dog, you might find out exactly when the plague is: it’s right now.
The First Great Disaster: The Justinian Plague (541–549 AD)
Before the Middle Ages even began to think about knights and cathedrals, the Byzantine Empire got hit by the first recorded pandemic. This is what historians call the First Pandemic. It started around 541 AD during the reign of Emperor Justinian I. It wasn't just a local outbreak in Constantinople; it tore through the Mediterranean, hit Persia, and even reached as far as Great Britain.
Procopius, a historian of the time, wrote about people seeing ghosts before they fell ill. He wasn't being literal—he was describing the delirium of high fevers. People would develop "buboes," which are basically just swollen, agonizingly painful lymph nodes in the groin or armpit. At its peak, some records claim 10,000 people were dying every single day in Constantinople alone. While modern historians like Lee Mordechai have recently questioned if the death toll was as high as traditionally thought, there’s no doubt it crippled the empire's ability to fight off invaders. It kept popping back up in waves for another two centuries. It didn't truly "end" until about 750 AD.
The Big One: When the Black Death Changed Everything (1347–1351)
This is the era most people are looking for when they search for when was the plague. The Second Pandemic began in the mid-14th century. It started somewhere in Central Asia—possibly near Lake Issyk-Kul in modern-day Kyrgyzstan—and hitched a ride on the Silk Road.
By the time it reached the port of Caffa in the Crimea, it was a weapon of war. There are famous (though debated) accounts of the Mongols catapulting plague-infested corpses over the city walls during a siege. Whether that’s 100% true or just a bit of medieval propaganda, the result was the same. The plague got onto Genoese trading ships.
From 1347 to 1351, it was absolute carnage.
You’ve probably heard the nursery rhyme "Ring Around the Rosie." People love to say it’s about the plague—the "rosie" being the red rash, the "posies" being herbs to mask the smell of death, and "ashes, ashes" being the cremation of bodies. It’s a creepy story, but folklorists like Philip Hiscock point out there’s actually no evidence the rhyme existed before the 1800s. Still, the reality was worse than any poem.
In Florence, the writer Giovanni Boccaccio described how people dropped dead in the streets. Neighbors only knew someone was dead because of the smell. This four-year window changed the world. Labor became scarce, which meant peasants could finally demand higher wages. The feudal system basically shattered because there weren't enough bodies left to till the land for free.
It Didn't Stop in 1351
The biggest misconception about the plague is that it disappeared after the Middle Ages. Not even close. For the next 300 years, Europe lived in a state of constant "plague watch." It became a seasonal visitor. London, for instance, had major outbreaks in 1563, 1593, 1603, 1625, and finally the Great Plague of 1665.
During the 1665 outbreak, the city lost about 100,000 people—roughly a quarter of its population in just 18 months. This was the era of the "Plague Doctor" with the bird-like mask. You’ve seen the costumes. Those masks weren't for fashion or to look scary; they were filled with aromatic spices like lavender and camphor because doctors believed "miasma" or bad air caused the disease. They were wrong about the air, but the thick leather robes actually protected them from flea bites, which is why some of them survived.
The Third Pandemic: The One Nobody Talks About (1855–1960)
If you think the plague is ancient history, you’re missing the Third Pandemic. This one started in the Yunnan province of China in 1855. Unlike the medieval version, this one spread globally via steamships. It hit Hong Kong, then Canton, and eventually reached every inhabited continent on Earth.
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This was the first time scientists actually figured out what was happening. In 1894, Alexandre Yersin, a Swiss-French physician, isolated the bacterium in Hong Kong. That’s why we call it Yersinia pestis.
This pandemic lingered for decades. It hit San Francisco in 1900, leading to a dark chapter of history where the city's Chinatown was quarantined and its residents were targeted by racist policies. Even though we had better medicine by the mid-20th century, the World Health Organization didn't consider the Third Pandemic "over" until 1960, when global cases finally dropped to a negligible level.
Why Geography Matters More Than Dates
When we ask when was the plague, we’re often really asking where was the plague. Because it moves. It’s a zoonotic disease, meaning it lives in animals. Specifically, it lives in rodents and is transmitted by the Xenopsylla cheopis flea.
- The Steppes of Asia: This is the ancestral home of the plague. It lives in marmots and ground squirrels here.
- Sub-Saharan Africa: Currently, the Democratic Republic of the Congo sees some of the highest case numbers in the world.
- The United States: It arrived in 1900 and never left. It moved from urban rats to rural rodents. Now, it's endemic in ground squirrels, prairie dogs, and woodrats in states like New Mexico, Arizona, and Colorado.
How to Identify the Three Main Types
It’s not just one disease. Well, it's one bacterium, but it presents in three terrifying ways.
Bubonic Plague
This is the most common form. You get bitten by a flea. Within a week, you have a fever, headache, and those "buboes." If you get antibiotics early, you’ll probably be fine. Back in 1348? Not so much. Mortality was around 60% to 80%.
Septicemic Plague
This happens when the bacteria skip the lymph nodes and go straight into the bloodstream. This is the stuff of nightmares. It causes "disseminated intravascular coagulation," which basically means your blood starts clotting inside your vessels, your skin turns black (hence "Black Death"), and your fingers or nose might literally rot off while you're still alive. It’s almost 100% fatal without treatment.
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Pneumonic Plague
This is the rarest but most dangerous version. It’s the only one that spreads from person to person through the air. It’s a lung infection. You cough, someone else inhales, and now they have it. If you don't get treated within 24 hours of the first symptom, you’re almost certainly going to die.
The Mystery of the "Plague Gaps"
One thing that drives historians crazy is why the plague disappears for hundreds of years. Why was there a gap between 750 AD and 1347 AD? Some researchers, like those studying ancient DNA at the Max Planck Institute, suggest the bacteria might have mutated to become less virulent, or perhaps human populations developed a temporary immunity. Others point to climate change. A slight drop in temperature can change how fleas behave and how many rodents survive the winter.
We also know that the plague of the Stone Age was different. Geneticists found Y. pestis in 5,000-year-old skeletons in Sweden. But that version didn't have the gene that allowed it to survive in flea guts. It had to be spread by direct contact. It wasn't until later that it evolved the "flea-power" that allowed it to wipe out entire civilizations.
What You Should Actually Do About It Today
Honestly, you don't need to lose sleep over a medieval revival. But you should be smart. In the modern era, "when" the plague happens is usually during the summer months in rural areas.
- Keep your pets safe: If you live in the Western US, use flea control on your dogs and cats. They can bring infected fleas into your bed.
- Don't touch dead stuff: If you see a dead squirrel or prairie dog on a trail, leave it alone. The fleas leave the body as soon as it gets cold and look for the next warm thing—which might be you.
- Watch for symptoms: If you've been hiking and develop a sudden, crushing fever and painful swelling, go to the ER. Tell them where you were. Common antibiotics like streptomycin or gentamicin work wonders, but only if you start them fast.
The plague isn't a ghost. It’s a biological reality. It has defined human history more than almost any war or king. While the "When Was the Plague" question usually leads us to the 1340s, the real answer is that it's a permanent part of our world's ecosystem. We didn't beat it; we just learned how to hide from it with better soap, better housing, and a really solid dose of tetracycline.
Practical Steps for History Buffs and Travelers
If you are traveling to areas where the plague is endemic—like parts of Madagascar, Peru, or the Southwest US—stay on cleared trails. Avoid "rodent-rich" environments. If you’re a researcher or student looking into this further, don't just rely on general history books. Look for "paleogenetics" papers. That is where the real timeline is being rewritten.
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Scientists are currently pulling DNA from the teeth of ancient skeletons to map exactly how this disease moved across the globe. We are finding out that there were "mini-outbreaks" we never even knew about. The timeline is expanding. Every time we find a new mass grave in London or a burial pit in Kyrgyzstan, the answer to when the plague happened gets a little more detailed and a lot more interesting.
Understand that history isn't static. What we "know" about the plague's timeline today might change next year when a new archaeological site is discovered. Stay curious, keep your distance from wild rodents, and remember that we live in a world where the deadliest killer in human history is now mostly just a footnote in a medical textbook.