I went shopping today to Ulm and parked about about 30ft under street level. Some old buildings are on display behind glass another 20 or so feet down. I can understand that people might reuse foundations over the centuries but how on earth is it that especially on a continuously inhabited site, that effectively one city can be built on top of another. What I mean is, the streets is Ulm must be 50 ft higher now than they used to be when the place first started!!! How does this happen?