The Caves Of Steel
All of this was contained in a habitable deck or shell fifty kilometres in diameter, wrapped around the nickel-iron keel on which Ophir had been founded. A surface area of eight thousand square kilometres. The overhead was more than a kilometre high, and there was weather beneath it. Shoals of wispy clouds; a dark rainstorm. Vast perspectives were interrupted by enormous bulkheads of diamond-fullerene composite pierced here and there by ship-sized airlocks through which rail cars and ground traffic passed.
Once, the rock at the centre of Ophir’s shell had been occupied by a single small, tented town and a scatter of vacuum-organism farms. And then the True Empire had absorbed it, and embarked on an insanely grand engineering project. Thousands of huge machines had processed primordial organic material mined from a score of comets, levelled the cratered terrain and covered it with densely woven layers of fullerene, and floated a shell a kilometre above this foundation, supported by bulkheads that divided the interior into a hundred segments, each landscaped with a different garden biome. A world-city. A monument to the Trues’ hubris.
It was the one of largest structures ever built in the Solar System, yet despite its adamantine foundations and bulkheads, and the deep layers of foamed fullerenes that formed the outer skin of its shell, it was hopelessly vulnerable. Its defence system of ablative lasers and swarms of bomblets and drones was sufficient to sweep and deflect debris from its orbital path, but offered no protection from a concerted attack.
The Trues had built Ophir as an act of ego and of defiance. To prove that they could; to prove that none of their enemies could challenge them. And their enemies had called it the City of the Caves of Steel because, like that ancient material, it was both massive and brittle. Collision with a single rock just a few tens of metres across would utterly destroy it. When the True Empire had at last fallen, the world-city had been spared only because a small majority of posthumans could not countenance the murder of several hundred thousand citizens. Five hundred years later, the descendants of those citizens were still forbidden to travel beyond the shell of the city’s overhead, and their numbers had been swollen by baseliners fleeing predatory dacoits and the capricious rule of posthuman clades. The magnificent folly of the True Empire had become a refuge and a prison.
From Evening's Empires