Cities have historically been centers of commerce, industry, and...disease. In the early 1800s, cities became so populated and densely packed that diseases began to spread at an unprecedented rate. All hope seemed lost until a series of critical scientific discoveries, which triggered a revolution in urban sanitation and health.

Read This Next

Zapping: The boisterous protest tactic that ignited early LGBTQ activism

Appalachia's wild rat is mysteriously disappearing—but the pandemic offered hope

There’s a new ocean now—can you name all 5?

Go Further

Subscriber Exclusive Content

Why are people so dang obsessed with Mars?

How viruses shape our world

The era of greyhound racing in the U.S. is coming to an end

See how people have imagined life on Mars through history

See how NASA’s new Mars rover will explore the red planet

Why are people so dang obsessed with Mars?

How viruses shape our world

The era of greyhound racing in the U.S. is coming to an end

See how people have imagined life on Mars through history

See how NASA’s new Mars rover will explore the red planet

Why are people so dang obsessed with Mars?

How viruses shape our world

The era of greyhound racing in the U.S. is coming to an end

See how people have imagined life on Mars through history

See how NASA’s new Mars rover will explore the red planet