Like many famous political institutions, the Berlin Wall is easy to talk about without knowing much about it. Like the French Revolution or the Roman Empire, once the wall is invoked, little more has to be said: Its reference is enough to confer meaning. On the 30th anniversary of its collapse, it’s worth examining what it really meant to the people who lived in its shadow—and what lessons we can draw today as new walls go up around us.

Construction of the Mauer began on August 13, 1961, on the East Berlin side of the East/West divide. Like all walls, it was not a single thing, but a set of things: a concrete edifice with guard towers, a thick internal zone (the death strip) and other security installations. This wall was not a joint endeavor. It was built entirely by East Germany (the German Democratic Republic, or GDR), designed as a bulwark against fascism, spies, and the dangerous capitalist ideology of the West, which might spread inequality into the GDR.

It was thus, ostensibly, a “people’s wall”—although most of the actual people didn’t see it that way. Prior to the wall’s going up, more than 3 million East Germans fled the GDR into West Berlin, from which they could travel to the West German mainland, and thereafter wherever they wanted. For all the government rhetoric about stopping evil Westerners from getting in, people immediately understood the barrier’s actual purpose: to keep East Germans from getting out.

The GDR was officially formed on October 7, 1949, heavily managed and controlled by Moscow. It didn’t take long before capitalist West Germany, which was widely successful in repairing itself after the war, grew apart from an East Germany that remained in shambles. Absent a wall, immigration restrictions were unable to stop people from crossing. The GDR set heavy penalties against leaving—what they termed illegal emigration (Republikflucht)—including several years of jail time. But these regulations were ineffective in an open, integrated city in which people could simply walk to the other side and vanish; simply put, it’s hard to punish people you can’t catch.

In the first years after the war, the inter-German border was relatively open, but in the early 1950s Stalin ordered it shut, and in 1952 the perimeter was lined with barbed wire. At that point, open Berlin became a big problem—not just for the GDR but also for the Soviet Union. In Berlin, people could escape to the West. But as importantly, they could also return to the East and talk about how much better conditions were on the other side.

And so, beginning at midnight on August 12, 1961, the East German army went about closing off the border. By the following morning, entire streets were ripped up (so cars could not cross) and barbed wire erected to prevent foot passage. Over the next weeks, this makeshift system was replaced by concrete blocks and standing units of military personnel, tasked to shoot anyone that tried to push through. Families were divided, employees separated from their jobs, and West Berlin became a foreign country: cut off from the East, and barricaded, like a capitalist island in an inhospitable socialist sea.

Unlike the walls we see today, which even border professionals admit are exercises in futility, the Berlin Wall was remarkably effective. From its inception in 1961 until its collapse in 1989, it prevented about 95 percent of all attempts at crossing, with only 5,075 people in total making it across (out of more than 100,000 attempts). Records vary, but there were at least 138 deaths. So what made the Berlin Wall work, as opposed to the myriad walls of today? Was the reason material, due to its insurmountable combination of concrete barrier and death strip, or tactical, as its urban location made it impossible to avoid detection? It’s hard to see these as sufficient explanations, given our own high-tech borders and gated border cities. Besides, one should never study an institution in isolation from the system of which it is a part; doing so risks overstating its primacy. So to understand the wall, you have to understand the GDR.

When we recall East Germany today, we invariably think of the ruthless internal security forces immortalized in the 2006 film The Lives of Others (directed by Florian Henckel von Donnersmarck). The Stasi was one of the most brutal security organs in world history, known for spying on its own population. Its official numbers were huge (numbering in the hundreds of thousands), but the body drew its principal strength from citizen-informants. In 1990, after the GDR collapsed, the Stasi archives revealed records on nearly 6 million citizens from a state with only 17 million people in total.

Stasi officials infiltrated nearly every corner of society. Agents were posted to schools and hospitals, industrial and agricultural enterprises, apartment buildings and social clubs. They were tasked with reporting suspicious activity, including that of family members and friends. Sometimes this surveillance was just aimed at getting information; at other times, it was to isolate people; but above all else, it was designed to breed fear. The idea was to make you believe you were being watched, that your face gave off clues as to the inner workings of your mind. This was done through insidious tricks, such as breaking into houses and rearranging furniture (so you come to believe you are being watched, or have gone crazy, or both), as well as classic bullying tactics, like threatening access to health care, or refusing a promotion without reason.

The Stasi state was so pervasive that few people weren’t either part of the spying network or blackmailed by it. By the time of the Mauerfall, there was about one agent for every hundred people. When you include all the informants, it is one for every 6.5 citizens.

During the course of this past year, I have interviewed many citizens of the former GDR, specifically refugees who had braved the Iron Curtain and escaped to freedom. Hearing these stories helps contextualize life there. Beginning in spring 1989, word began to spread about political liberalization in other Eastern Bloc states, notably Hungary, including at the edges of the Iron Curtain itself. As life in East Germany became increasingly unbearable, families began packing up and traveling to the Hungarian borderlands in an effort to escape West.

Planning an escape was not easy, and took place in extreme secrecy. What might happen if they got caught? One recurring fear was about schooling. If they were caught, their kids would be punished first: they might be penalized on their exams, barred from advancing, humiliated. No one wants their children treated this way. But what future could they have if they stayed? It was an impossible bind.

One of the East Germans I spoke to couldn’t sleep the whole month before the trip, relying on painkillers from her husband’s dentistry practice. Those days were minefields of emotion, of sideways glances out the window or down the street. No one could know, not even close friends. And as anyone who has ever held a secret can appreciate, the power of not talking is debilitating—especially in a place like this, where if anyone found out, it could be their ruin.

These accounts are harrowing, but common to them all is the rationale for leaving: It wasn’t the wall so much as the corrupt, brutal state itself. The wall was the symptom; the GDR, the disease.

As other Eastern Bloc countries began to reform, the Stasi grew more ruthless, breaking up vigils and demonstrations, and sanctioning police brutality against nonviolent protesters. Pressure mounted, and the popular rejection of the GDR became increasingly prominent; starting in September 1989, in the city of Leipzig, there were giant rallies every Monday at St. Nicholas Church, gaining strength and prominence with each passing week. On November 4, more than half a million people gathered in Berlin’s Alexanderplatz to demand change. The following week, the wall came down.

There too, it was not just the wall people cared about. In addition to calls for reunification, at the protests were myriad signs decrying abuses of power in the GDR: “No more privileges! We are the people!” (privilegien weg! Wir sind das volk!), demanding “new choices for a new way” (neue wählen für einen neuen weg). But the wall had to come down first. Without it, the state couldn’t hold anyone in.

Looking at footage of the Berlin Wall coming down is emotional, even today. The joy is so pure, and the optics so clean: The wall signified enclosure and the horrors of authoritarianism; its fall was a victory for democracy and liberalism.

And yet the wall’s legacy has never been more contested. Across the West, we see a return of physical walls and xenophobia, along with ever more sophisticated surveillance at home. What, then, can the Berlin Wall tell us about the wall we see on the rise on the US-Mexico border today—or any of the numerous other walls being built worldwide?

We should be careful in forging comparisons. They were very different kinds of walls. The Mauer was meant to keep people in; our wall is designed to keep people out. They were completely discrete in terms of structure and purpose. Certainly, defenders of the present US-Mexico wall should keep this in mind before arguing that “walls work, look at Berlin.”

Instead, a different conclusion obtains: The Berlin Wall was so effective mostly because it was part of a comprehensive system of surveillance and control. As my GDR interviewees detail, it took immense courage to even think of scaling the wall—or piercing any other part of the Iron Curtain—not just because of the threats inherent to the crossing (which were myriad), but because of the lengths one would have to go to to get there. Stasi control was so complete, most people never dared. They were so sure of being found out that actually drawing up plans to hazard the wall was but a distant dream.

It is this more than anything else that gives us pause about our present, given the pervasiveness of surveillance in the United States and the rise of data analytics in statecraft. The United States today uses technologies of control beyond the Stasi’s wildest dreams. We tend to think the questions of the wall and surveillance are separate, but perhaps we shouldn’t. It’s the combination of the two that places our civil liberties most at risk.

As citizens, we are caught between a wall and a web. Our situation is leagues behind that experienced in the GDR. But if we’re not careful, we may find ourselves slipping that way as well.