Rocks were an essential element in most attacks on Xeelee concentrations; they provided cover, resources, and soaked up enemy firepower. But while most Rocks were purposefully deflected onto their required trajectories, Orion Rock, and a number of others, had natural orbits that took them into useful positions in the Core without deflection. So they could be used as cover, to mount covert operations.
But as the Core's geography spanned light-years, travel times were painfully slow. The planners behind this place had been forced to think ahead, across no less than a thousand years—for that was how long Orion Rock would have to travel before it was in a position to be useful.
Nilis said gravely, 'This is the scale of this war, Pirius. Orion Rock is like a generation starship sent to war: forty, perhaps fifty generations doomed to these dark tunnels, all the possibilities of their lives sacrificed to one goal, a strike on the Xeelee, a single assault that might be carried out in their children's time, or their children's children.
'A thousand years, though. On pre-Occupation Earth, a thousand years was a long time: time enough for empires to rise and fall, time enough for history. To us it is just a checkmark on a war planner's chart!'
-Exultant, Ch. 48