Recreating Basel’s lost city walls with GenAI

I've always been fascinated by the shapes of historic buildings, particularly the awkward, half forgotten ones that linger in modern cities as if they are quietly waiting for someone to notice them. Switzerland is wonderful for this because so much of the country escaped the destruction that erased huge parts of other European cities during the twentieth century.

Basel carries that sense of survival especially strongly. For all its contemporary ease and elegance, this was once a proper fortified place with walls and gatehouses and a skyline that was far more practical than picturesque. A castle city in everything but name.

Walking through Basel’s medieval ghosts

I realised recently, when I wrote about climbing up to Neu Falkenstein, that I have this habit of mentally rebuilding old structures wherever I find them. Ruins trigger it most obviously, but Basel does it too. Whenever we pass one of the three surviving medieval gates, something in me clicks into gear and I slide into a kind of gentle fatherly commentary mode.

The children have heard it often enough. Imagine this when it was the edge of the city. Imagine guards on the walkway above. Imagine fields stretching out behind us rather than tramlines and apartment blocks. They humour me with the sort of patience that children reserve for their parents’ mild obsessions, but I like to think that a little of it seeps in. These gates are not decorative leftovers. They are fragments of a world that once set the rhythm of life here.

A city that used to be walled

The thing about Basel that always catches me off guard is how quietly it holds onto its past. Long before anyone thought of it as a cultural hub, it was a smaller and much more defensive place, wrapped in thick stone walls that kept things safe and orderly. As the city grew across the centuries, those walls expanded with it. A small inner wall at first, then a larger one, and eventually a full outer ring built in the late fourteen hundreds after the earthquake reshaped the place.

Spalentor, St Alban Tor and St Johanns Tor all belong to that later phase, the era when Basel began to look outward with a bit more confidence. Most of the walls were removed long ago once they became more obstacle than protection, which is why the three surviving gateways feel so striking. They are the last sentences of a much longer architectural story.

Rebuilding the past, imagining the future

This curiosity finally pushed me to try something new. I decided to recreate the approach to Spalentor using DALL E, treating it like a small creative experiment to see whether I could coax the past back into view. It took several attempts and more prompt crafting than I care to admit, but eventually the images began to feel atmospheric and lived in.

Definitely not perfectly accurate, because AI cannot resist a dramatic sky or a bit of tidy medieval flair, but close enough that my imagination could fill in the missing pieces. Suddenly I could picture Basel not as a museum set piece but as a working city gate where travellers approached from dusty roads, carts rattled across uneven ground and smoke drifted from chimneys on the inside.

It made me wonder what someone six hundred years from now will make of us. We piece together medieval life from stones and fragments and a handful of written accounts. They will have video records, aerial images, building scans and a near infinite trail of digital traces. They will be able to reconstruct our age with extraordinary clarity, yet I suspect they will still squint at whatever remains and try to imagine the bits the data cannot quite express, just as we do now. That human instinct to rebuild the missing parts feels timeless.

A city with layers

If any of this interests you, the Historisches Museum Basel on Barfüsserplatz is well worth visiting. It has the kind of objects and models that make the past feel physical, the sort of details that explain how the city once fitted together and how these gates connected to the world beyond. You go in expecting a quick look and find yourself wandering through a miniature version of Basel, the old and the new layered together.

Walking past Spalentor now, after this little experiment, I find myself thinking not just about the world that has been lost but also about the world that has yet to come. These old stones remind you that cities are long conversations, and that every generation adds something to the shape of the place.

We are borrowing Basel for a while. Someone in the future will inherit whatever remains and try to imagine us just as we try to imagine the people who passed through that gate centuries ago.