In addition, this society practices extensive thought control - to stray beyond what is acceptable is heresy. The bastion of technology and slave society are separated by distance and natural barriers. The bastion of technology controls an underground world subway system, so they can control access. Distance and the desert separate the two places. Bartertown is walled-in.
Water separates places.
The town is walled-in. Where does the hero come from The hero is an astronaut who comes from the earth's past. The hero is revived from suspended animation, from the past. The hero is ambushed and lost in the desert when he comes to Bartertown. On two more occasions, he is stuck in the desert and ends up in Crack in the Earth and then back in Bartertown.