This is for the firemen of California and neighboring states who fought the fires of October 2003, with particular thanks to those who saved our house and others in Indian Falls, Chatsworth, Los Angeles County.

The Ringworld is about the same mass as Jupiter. Its shape is that of a ribbon a million miles across and six hundred million miles long, which makes it a bit larger than the Earths orbit, and a few miles thick. It circles a yellow dwarf star. Its spin, at 770 miles/second, is enough to give it about Earths gravity of centrifugal force. Walls along both rims, standing a thousand miles high, are enough to hold an atmosphere for millions of years.

Much else derives from these basic assumptions.

The inner surface is a habitat three million times the area of planet Earth. The topography is literally a work of art, carved in by whoever built the thing, so that from underneath the Ringworld resembles the back of a mask.

An inner ring of shadow squares block the sun, giving periods of night; else it would always be noon. A system of pipes leads from the bottoms of oceans, under the Ringworld floor, up the back of the rim wall and over the edge, to recycle seabottom ooze (or flup) into spill mountains. Huge attitude jets stand atop the rim wall, Bussard ramjets using the solar wind of protons for their fuel, to hold the Ringworld against its inherent instability. There are spaceport ledges outside the walls. Two vast salt oceans serve as preserves for seagoing life, and as something more: maps of several worlds at one-to-one scale. The Ringworld floor is of unnaturally strong material, dubbed scrith, with other unusual properties.

The sun itself is involved in the Ringworlds meteor defense. A superconducting network embedded in the Ringworld floor generates a superthermal laser effect in a solar flare. The drawback: it cant fire through the Ringworld itself. Thus any meteorite that strikes the Ringworld, such as the one that made Fist-of-God Mountain, generally rams upward from underneath.