From what I understand, this happens in Rome all the time. Their subway system encounters a work stoppage due to stumbling onto a new buried building on like a weekly basis. Rome keeps sinking and so there are layers upon layers of buildings on top of each other. While there last May I went to a 14th century chapel they was on top of a fourth century chapel, on top of a send century chapel, on top of a first century villa, on top of an old mint. There is an underground river that would need to be diverted to see if there is something under that but it appears there is.

Fun thing I saw there: this is where St. Cyril was buried and above his tomb there are about a dozen plaques thanking him for bringing literacy to places like Ukraine, Macedonia, etc. Despite them being centuries old I could read them almost perfectly since I can read Russian and Ukrainian. That was incredible.