"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).