The Black Death (1347-1351)
Bubonic plague, carried by fleas on rats, swept through Europe starting in 1347. It killed an estimated 25 million people — roughly a third of Europe's population — within four years.
The death toll reshaped labor, economics, and social structures across Europe.
Cities began developing quarantine systems and sanitation practices, a slow recognition that urban cleanliness affects disease.
Rats aren't just a nuisance; historically they've been a disease vector. Philadelphia's city government is treating its rat problem as a public health issue, not just a cleanliness complaint.
