> When most cities build metro systems, they simply blast through rock.

I'm not sure that this is true (ignoring the bit about blasting, which hasn't been a standard way to build metro lines for a very long time, of course); there was a lot found when London's Crossrail was built, say.

(While it's not made totally clear, I assume they're mostly finding stuff building stations, not tunnels. The tunnels are ~20m below ground, but the stations have to go all the way to the surface.)

Really, any old city, anytime you build anything you may find something. For instance, here's a supermarket with bonus Viking ruins in Dublin: https://www.atlasobscura.com/places/aungier-street-lidl-arch...

In Sofia we have roman ruins everywhere around metro stations https://archaeology-travel.com/bulgaria/serdika-ii-metro-sta...

In the same vein, Bloomberg office in London UK has an Ancient Rome museum and the access is free: https://www.bloomberg.org/arts/advancing-the-arts-around-wor... (disclosure: I work for Bloomberg).

For reasons, I used to go to Rome quite frequently in the 2010s, and the construction of Metro C was already a meme. But now some of the stations are quite interesting indeed.

It's quite interesting to see how much earth is typically above ancient ruins. Cities built upon cities for 1000's of years where a street or building was once at ground level and now is 2-4 stories beneath our modern world.

While visiting Vienna, there are ruins on display in Michaelerplatz (central Old City), so cool.

Thessaloniki had the same issue, and now there's a stop where you have walkways above the ruins.

Some photos of the "before" here:

https://www.thessalonikiguide.gr/metro-thessalonikis-mia-arx...

Okay, I'll say it: is it really worth encumbering the movements of millions of people for decades in order to make a few boring history exhibits? If you want to see some the bone comb that belonged to somebody's great^100-grandmother, there are dozens of museums that already have one on display.