"We came back [from Mars]," Pris said, "because nobody should have to live there. It wasn't conceived for habitation, at least not within the last bi… - Philip K. Dick

"We came back [from Mars]," Pris said, "because nobody should have to live there. It wasn't conceived for habitation, at least not within the last billion years. It's so old. You feel it in the stones, the terrible old age. Anyhow, at first I got drugs from Roy; I lived for that new synthetic pain-killer, that silenizine.
And then I met Horst Hartman, who at that time ran a stamp store, rare postage stamps; there's so much time on your hands that you've got to have a hobby, something you can pore over endlessly.
And Horst got me interested in pre-colonial fiction."
"You mean old books?"
"Stories written before space travel but about space travel."
"How could there have been stories about space travel before - "
"The writers," Pris said, "made it up."
"Based on what?"
"On imagination. A lot of times they turned out wrong [...] Anyhow, there's a fortune to be made in smuggling pre-colonial fiction, the old magazines and books and films, to Mars. Nothing is as exciting. To read about cities and huge industrial enterprises, and really successful colonization. You can imagine what it might have been like. What Mars ought to be like. Canals."
"Canals?" Dimly, he remembered reading about that; in the olden days they had believed in canals on Mars.
"Crisscrossing the planet," Pris said. "And beings from other stars. With infinite wisdom. And stories about Earth, set in our time and even later. Where there's no radioactive dust." [...]
"Did you bring any of that pre-colonial reading material back with you?" It occurred to him that he ought to try some.
"It's worthless, here, because here on Earth the craze never caught on. Anyhow there's plenty here, in the libraries; that's where we get all of ours - stolen from libraries here on Earth and shot by autorocket to Mars. You're out at night humbling across the open space, and all of a sudden you see a flare, and there's a rocket, cracked open, with old pre-colonial fiction magazines spilling out everywhere. A fortune. But of co