Walls:Civilizations surround themselves in walls. They raise walls against enemies, against the environment and against the spirit world. In this classic episode, Robert and Julie examine walls, from Ming Dynasty battlements to the galactic borders of our universe.
Learn more about advertising on the HowStuffWorks podcasts at www.howstuffworks.com/advertisers.htm
And to learn about your ad choices when listening to podcasts, visit
https://www.howstuffworks.com/privacy.htm#ad-choices
