Border walls and fences have proliferated during the 21st century – quietly, in countries such as Saudi Arabia, Thailand and Jordan; loudly, in Israel, Hungary and the United States. The policy of building barriers is nothing new. Cities first began girding themselves with walls nearly 12,000 years ago, and larger states have been at it for at least 4,000 years. Razor wire, electronic sensors and concrete slabs have supplanted mud bricks and tamped earth. Otherwise, we are carrying on much as we always have.
Innumerable battles were once fought at walls; invaders and defenders clashed at the boundaries of cities, kingdoms and empires. In the 21st century, those battles have turned political. The most bitter fights now occur over proposed walls – which, for the first time, are debated in…
