A bone idol must be constructed with utmost care, using a piece of bone from each of the dead intended to be bound by it.
Placed in a central location, the bone idol's influence will reach to any relevant corpses within its radius. As long as the idol is in place, any skilled necromancer may control the corpses in question. Great care must be taken to protect the idol, lest some damage may come to it and all control of the corpses be lost forever.
Constructed in the left hall of the mines, the bone idol's reach will be sufficient to affect all miners.