 This is a weird one here. See if you can follow me. This takes place thousands of years in the future when a distant planet has been colonized by earthlings who commissioned the most advanced robotic computerized cities ever conceived, but being religious they programmed these computer-controlled cities with the ability to pass judgment on citizens and banish anyone who was considered a sinner. So of course the various cities of the world once they've got online they compared notes and determined that they were filled with sinners and banished all humans to the wilderness. So a thousand years later humans are living like primitive cavemen in the jungles and in the deserts while these beautiful eternal pristine self-perpetuating cities sit empty. The most vivid idea about this concept though is the way in which these living cities, even though they're empty of humans, when they use up the resources in their area they pick themselves up, break up into thousands or even millions of constituent parts and march across the planet until they find a favorable location. Very vivid, very memorable imagery. I read this book back in the 80s, not long after it was first published and just the idea of these migrating cities stuck with me. The rest of the book I didn't remember at all. That's why I wanted to get it and read it again, and I'm surprised that nothing else stuck with me because there's a lot of interesting stuff in this book. It's really strange and it has a really strange ending too. And of course it's Greg Baer, so it's well written. I recommend it. You can support 30 Seconds Sci-Fi and my other projects by becoming a patron. There's a link in the description below. And visit the 30 Seconds Sci-Fi Tumblr. That's my headquarters. In addition to my videos, I publish links and updates there every day.