As the Umbrella Movement Visual Archives and Research Collective no doubt hopes will one day be the case for the artwork that can be found on the streets of Hong Kong today, the murals and graffiti painted and sprayed on the western facade of the Berlin Wall are likely to feature heavily in its commemorations; the contribution of French street artist Thierry Noir has already been feted at a recent retrospective in London.

The white line is unlikely to play a part and yet its story tells more about what that wall did - and still does - to people than any other public artwork ever has.

All five of the wall-painters had been born in East Germany, in Weimar, but had begun to rebel against the communist regime's social norms in their late teens. Frank Willmann read Nietzsche and Solzhenitsyn, his friend Frank Schuster wore sandals and string vests. Wolfram Hasch grew his hair long. Jurgen Onisseit played in a punk band called Creepers. Thomas, his younger brother, was arrested for spraying dadaesque slogans such as ("Turn the state into cucumber salad") on to walls around Weimar.

The regime's tolerance for alternative lifestyles was low. Between 1983 and 1985, after a series of run-ins with the authorities, the five friends were all granted permission to resettle in the west and moved to Berlin.

The wall stayed with them, however. Years after the five men had crossed over from east to west, they would still dream about it. Willmann says he often found himself back in the old town centre of Weimar, having to somehow find an escape route to west Berlin. In some of the dreams, he'd manage to evade the border guards. In others, he'd get shot in the back, blown to pieces by landmines or mauled by dogs.

Talking to the wall-painters almost 30 years after the project, it is noticeable not only how much detail from that day they still remember, but also the different reasons they had to draw the line in the first place. For Willmann, now a journalist and author, the line was, above all, an artistic statement, a protest against what other artists were doing with the wall.

"For the rest of the world, the wall was little more than a big canvas. They just didn't care what was going on behind it. I particularly didn't like that [American artist] Keith Haring was given a special section of the wall all to himself, seemingly tolerated by the GDR [German Democratic Republic - East Germany]. We enjoyed painting a line through that one."

For Thomas Onisseit, who is now a graphic designer and lives in Dresden, the line was political rather than artistic, a way of sticking it to the regime in the east: "Going up to the wall for us was empowering - a reminder that we had made it over to the other side. When you'd feel low, you'd sit down by the wall with a six-pack of beer and start to feel better."

For Schuster, the line was political, too, but more of a protest against the complacency of the west.

"The leftists in west Berlin never understood why we had escaped from the east," says Schuster, now a university lecturer, sitting in a cafe by the river Spree. "They thought we had voluntarily left behind paradise. Some thought that made us Nazis. So we wanted to show them up a bit. To me, there was a difference between living in the east and in the west, even if just a small one. In the east, I could take one step before someone stepped on my toes. In the west, I could take two."

All of them agree that it was the older Onisseit brother, Jurgen, who had the idea. He painted a manifesto on the wall next to the start of the line: "This line will demarcate the Berlin area anew and reveal the wall as a ghetto wall. Its beginning and end is here."

"Jurgen had integrity, he was a doer," says Schuster.

"He could be very spontaneous, and that could be very intoxicating," says Willmann. "If he had an idea, you knew it was doable."

It wasn't until 2010, when Willmann started ordering up documents from the Stasi (the East German state security service) archive for a book about the project, that he realised the white line had yet another meaning for the leader of their group.

Between autumn 1981 and his transfer to the west in 1985, Jurgen Onisseit had worked as an or "unofficial collaborator" for the secret police, supplying information about Weimar's alternative youth scene. By naming a group of people involved in the "Turn the state into cucumber salad" stunt, he had indirectly brought about his younger brother's imprisonment.

For Jurgen Onisseit, was the white line an attempt to literally "draw a line" underneath his Stasi past? If so, it failed: a new documentary, ("Drawing a Line"), by director Gerd Kroske, portrays Jurgen and Thomas' attempt and failure to cross over the dividing line still running through their family. In the film, the older brother is asked if he regrets betraying his friends.

"Betray my friends?" Jurgen says. "I don't have friends."

The white line on the Berlin Wall had one other meaning. On the eastern side, border guards used white paint to reiterate the "anti-fascist barrier" against the west. When the five masked men with the buckets of white paint were first spotted on the morning of November 3, it seemed obvious to them that the white line was no art project or political protest, but the state enemy in disguise, attempting to redraw the physical border between east and west.

As a consequence, border guards were ordered to slip through a hidden door in the Berlin Wall the next morning and ambush the painters. Four of the friends escaped, but Hasch was seized and pulled back into the east, where he remained in prison for three months before being released back to the west. For him, the group's ultimate nightmare had become a reality. He is the only member of the group who declined to be interviewed about the white line, either for the documentary or for this article.

"A line is a dot that went for a walk" is how German painter Paul Klee once described the act of drawing. In the logic of the Berlin Wall, even as innocent a definition of creativity as that amounted to a criminal act.

Guardian News & Media