Similar: NYC is absolutely riddled with tunnels and underground infrastructure: subways, power, sewage, and as I recall, deepest of all the projects which transport Catskills water into the city. I seem to recall a graphic which showed these tunnels at various depths, but have been unable to find it via numerous searches. There is a pretty cool spread at Gizmodo showing the East Side Access project for the LIRR thoug…
I believe this maybe the image you're referring to. http://www.nationalgeographic.com/nyunderground/docs/nymain....
> in very old cities ... running into an interesting archaeological site Why are archaeological sites are so far underground? Are ancient cities actually getting higher in altitude as old ruins get covered up? Why Pompeii was buried is clear. I am more curious about continuously occupied cities like Rome. How did the ruins get underground there ? The best answer I could find was this: http://www.straightdope.com/colu…
Don't forget that things aren't the same everywhere. The land in Alaska and New York is rising pretty fast, geologically speaking, since the weight of glaciers came off. Meanwhile New Orleans is sinking. Chicago took matters into their own hands and raised street level an entire floor to combat flooding. We still have ancient caves at ground level in New York, but I'm sure stuff buried under a city survives better.
"raised street level an entire floor to combat flooding" - yup, that's pretty much the same technique by which "the ancient cities are rising." Except that Chicago was lifted up, whereas the old cities were only readjusted - essentially, ground level becomes the first basement, entrance is now on what used to be second floor. This process could be repeated, giving rise to old ground-level floors becoming the third basement or similar. Case in point: Prague's Old Town, founded at riverside, was gradually raised by up to 30 feet (which has unexpected consequences, and actually worsens the flooding problems it was always expected to solve).