Several years ago, an episode of the TV show "Ghost Whisperer" was presented in a "pop up video" format. Throughout the episode, little bubbles would pop up on the screen containing interesting facts. One of these bubbles said something about the idea of a city being built on top of another city, with Ventura being cited as one of two examples of this concept. (I think Edinburgh was the other one.) Does anybody have any idea what this could possibly mean? I haven't been able to figure it out.