Since ancient times, border walls have simultaneously assuaged and stoked our fears of outsiders. But a history of walls can't tell the full story of civilization.
Three years after India and Bangladesh exchanged exclaves to simplify the world's most complex border, many who chose to move rather than to change their citizenship find that their prospects are not what they'd hoped.
San Luis, Arizona: A United States Drug Enforcement Administration official aims a flashlight down a 55-foot-deep drug-smuggling tunnel that spans a distance of nearly 240 yards under the U.S.-Mexico border. Drugs ran north, and weapons and cash ran south.