How many years did the Berlin Wall stand?

How to get close to this number

Subtract the dates. It went up in 1961 and came down in 1989, which is a difference most people can do from memory because both years are among the best-known in twentieth-century history.

The framing in the explanation is the one that lands: it has now been gone for longer than it existed. A structure that defined the political geography of a continent stood for less than three decades, which is shorter than the careers of many of the people who negotiated around it.

The speed of its construction is the other striking detail: the border was sealed with barbed wire in a single night before any concrete arrived. Physical barriers are usually understood as permanent infrastructure, and this one demonstrates that a border can be created overnight and removed within a lifetime — which is why it is the standard reference for how contingent political geography is.