Yet even in era of jet aircraft, helicopters, and drones––where walls can simply be flown over––there are still plenty of examples of effective walls. The Berlin Wall wasn’t erected in August 1961 to keep people out, even if the East Germans did say it was to keep East Berlin safe. The point of the wall was to keep people in.

The 96-mile wall, which in essence circled West Berlin, began as little more than barbed wire, but by the 1970s had become several layers deep. That included 116 guard towers and 20 bunkers with hundreds of guards. Yet from 1961 to 1989, more than 5,000 people did successfully manage to cross the border into West Berlin.

A final consideration includes two examples noted recently by Fox News––one in Hungary and another in Israel. The former was built in 2015, when tens of thousands of foreign citizens from the Middle East made their way to Hungary from Serbia and Croatia. In response, border walls were erected. According to Hungarian Foreign Minister Peter Szijjarto, the number of illegal migrants has dropped to almost none.