The day the Wall fell, I split up with my girlfriend. She had moved to a different city, and the long-distance thing wasn’t working; I went to visit her that Thursday evening, and we had an intense conversation over drinks and pizza, vaguely aware that people were staring at the television screens but assuming it was some sports event. By the time we had worked out that we had both reached the same conclusion about the future of the relationship, I had missed the last train; we went back to her place, I slept on the couch and got up early to go home. And then I bought a newspaper and discovered that while one (short and mostly sweet) chapter of my life was ending, the world had changed forever.

I first went to Berlin in 1986, over the long weekend of German Unity Day which was then on June 17, hitch-hiking there with a friend who I was working with in Heilbronn way off in the southeast. In those days Berlin was a slightly hippyish enclave (the hostel we stayed in was very hippyish and slightly threatening) on the front line of the Cold War. The inner German border remains the most vigorously fortified frontier I have ever seen. We went east as well as west (by tram to Frieedrichstraße), and took pictures of the Brandenburg Gate from both sides which I guess I must still have somewhere; I went to an eastern bookshop and made the mistake of referring to "Ost-Berlin" (rather than "Berlin, Hauptstadt der DDR"). At that point the Wall had been up for almost 25 years and looked like it would remain a lot longer.

I went back with Anne in 1992. It was utterly transformed, of course. I cried as we walked through the Brandenburg Gate, which had appeared so utterly blocked by historical circumstance and concrete fortification only a few years before. The west of the city had found a new security and confidence, a strong sense of liberation; the east was still shell-shocked by defeat. The transport system, now unified, charged considerably less to former easterners buying tickets. The frenzy of new build was just getting going but the momentum wasn’t yet there. Since then I’ve been back perhaps half a dozen times. Earlier this year I took an afternoon to retrace the Wall, helpfully marked out by bricks in the road. It remains a fascinating city for me, and every time I go I find something new.

The BBC has a handy list of walls that remain, including two of which I have direct experience (Belfast and the Green Line in Nicosia) and another which I work on (the Moroccan berm closing off the illegally occupied part of the Western Sahara). Just as the Berlin Wall disturbed me in 1986, any restriction like this disturbs me now. Robert Frost wrote "Something there is that doesn’t love a wall"; his New Hampshire boundary markers were threatened by natural forces, perhaps elves, built by old stone savages. The conflict-built walls of the world are also perpetually under threat from the erosive force of history. And a good thing too.