Strata is a comic science fiction novel by Terry Pratchett. Published in 1981, it is one of Pratchett's first novels and one of only two purely science fiction novels he has written, the other being The Dark Side of the Sun.
Although it takes place in a different fictional universe and is more science fiction than fantasy, it could be said to be a kind of prequel to the Discworld novels, as it also features a flat Earth similar to the Discworld. It has been called a "preconsideration" of Discworld, though the plot is modelled on (or parodies) that of the novel Ringworld by Larry Niven.
This planet is artificial, a flattened version of the medieval Eastern hemisphere of Earth. It rotates inside a gigantic hollow sphere with tiny "stars" affixed to the interior, with a small sun, moon and planets orbiting it.
After their ship is hit by an orbiting "planet", Kin, Marco and Silver are forced to land on the flat Earth. A return from the flat Earth seems impossible, unless they are able to find its mysterious builders, so they embark on a journey to the structure at the hub of the disc, the only thing which does not match geographically with the Earth they know. En route, they encounter the superstitious Middle Ages inhabitants of the disc, who believe the end of the world is coming about, due to the disappearance of one of their planets and the devastation caused by the ship's crash. They also discover a number of other differences. Rome exists - but only since in this universe our 'real' Rome was named Reme. Since only the Eastern hemisphere of Earth is represented, the continent of America is completely missing; the travellers encounter a Viking ship headed west and rescue it from falling over the rim of the world. The "planet" Venus does not have a moon.
In addition, there are real "magical" creatures and objects here, demons and magic purses and flying carpets - all of them, the travellers realise, highly advanced and sophisticated technological constructs like the disc itself. Indeed, the planet itself is an extremely old and complex automated system. The characters come to suspect that the builders of the flat world in fact constructed the universe as a whole, with the evidence of previous races being hoaxes and the flat world being an in joke.
Kin and the others eventually reach the hub and Kin makes contact with the planet's controlling systems. She is told that, lacking maintenance, the flat Earth threatens to fall apart. The machines offer their advanced technology, in exchange for Kin's construction of a real replacement Earth for the flat planet's inhabitants. Kin agrees; the implication being that the world she will build is our own Earth.
Humanity appears to be merely the latest of a long series of intelligent species who have evolved, altered the universe to better suit themselves, and died out before the next species arose. Before humans, there were the Great Spindle Kings, a race of acutely claustrophobic telepaths, who lived only a few hundred to a planet and therefore built entire planets from scratch to accommodate their population. Before them were the Wheelers, who were themselves preceded by increasingly alien races extending all the way back to the Big Bang.