THERE was a wall. It did not look important. It was built of uncut rocks roughly mortared. An adult could look right over it, and even a child could climb it. Where it crossed the roadway, instead of having a gate it degenerated into mere geometry, a line, an idea of boundary. But the idea was real. It was important. For seven generations there had been nothing in the world more important than that wall. Like all walls it was ambiguous, two-faced. What was inside it and what was outside it depended upon which side of it you were on. Looked at from one side, the wall enclosed a barren sixty-acre field called the Port of Anarres. On the field there were a couple of large gantry cranes, a rocket pad, three warehouses, a truck garage, and a dormitory. The dormitory looked durable, grimy, and mournful; it had no gardens, no children; plainly nobody lived there or was even meant to stay there long. It was in fact a quarantine. The wall shut in not only the landing field but also the ships that came down out of space, and the men that came on the ships, and the worlds they came from, and the rest of the universe. It enclosed the universe, leaving Anarres outside, free.

-- Ursula K. Le Guin "The Dispossessed"