Building walls that separate us from others is as old as humanity.

People have built walls to keep others out for thousands of years, from the Great Wall of China to Hadrian's Wall to security fences along the US-Mexico border. But did you know they've also been built to keep people in, to grow food, to control nature and to collect taxes? Sometimes they've helped people and kept communities safe, but they've also created inequity and done more harm than good. Why do we have walls at all?

Walls: the Long History of Human Barriers and Why We Build Them explores the many reasons humanity has put up walls over the course of our history, and why we continue building them today.