According to one Norse myth, the gods needed a wall. Asgard, their kingdom, had once been surrounded by barricades, but a war had destroyed them. When the gods decided to erect a new wall, a builder appeared out of nowhere and offered his services. Loki, the trickster, suggested that the gods accept his proposal but set an impossible deadline. When time ran out, they could send him on his way, thereby getting the lion’s share of the wall for free.

The builder accepted the terms and set to work. Accompanied by his trusty horse, he made quick work of the wall; he was perilously close to completing the stone loop around the kingdom before his time was up. Desperate, Loki transformed himself into a mare to lure away the builder’s horse. The builder was outraged. This was when the gods realized, to their horror, that he was actually a giant — their sworn enemy — in disguise.

The fence at the border checkpoint between Storskog, Norway, and Borisoglebsk, Russia © Lev Fedoseyev/ITAR-TASS/Alamy

Thor bludgeoned the interloper to death with his hammer. The wall remained, but the gods’ dishonest dealings set in motion Ragnarok: the fall of the empire and the end of the cosmos.

Border walls have been around as long as the gods themselves, guarding our cities and castles. They fell briefly out of favor, but at the moment, they seem to be enjoying increased popularity in such far-flung locations as Myanmar, France, Bulgaria, Pakistan, and, of course, the United States. Unlike those of yore, erected to keep out marauding invaders, today’s walls are designed to guard against desperate refugees and migrants. Governments are launching efforts to strengthen overburdened borders as people seek to escape everything from war and famine to drought and rising seas.

This revival comes at a time when the argument against walls seems particularly convincing: experts have found that walls have never really worked, and they often seem to presage not an empire’s perpetuity but its collapse. Walls offer the promise of absolute protection, but they almost always fail to deliver. Still, we build them again and again. Last winter, I traveled to Norway to see one of Europe’s newest and most infamous projects in hopes of learning what it could tell us about our age-old impulse to both wall ourselves off and wall ourselves in.