A fictional place in the asteroid belt in the Known Space series by Larry Niven.
When the belt was first explored, a roughly cylindrical nickel-iron asteroid, 2 miles by 1 mile, was found, close to Ceres. It was registered as S-2376.
In 2046, a crew of terrans arrived and claimed it for the belt. A hole was drilled down the axis of the asteroid and it was filled with plastic bags of water, then re-sealed. Jets were mounted to spin it on its axis. As it spun, solar mirrors heated it and the expanding water transformed the nickel-iron-composite, turning it into a bubble 12 miles long and 6 wide.
The bubble was set to rotate, generating half a G of gravity. The inside was filled with water, air, meteorite material and bacterial matter, as to make it habitable. In the middle, a special (permeable by certain wavelengths of light) fusion tube was placed, along the axis. Then, a bulge in the middle of Confinement makes a lake/river around the world. Finally, the ends are cooled to make for snow, and thus, water recycling.
Confinement was finished in 2071, freeing the belt from its last dependency on Earth: Women cannot have children in free fall. At any given time, there are roughly 800,000 people on the 200 square miles of land.
Audited July 5, 2002