A group that wished to be 'ever-living' instead was cursed with 'never-dying'. Thier flesh rotted and fell fromthier bones but still they lived on. Now as skeletons they continue thier quest to remove thier curse. As skeletons they differ in that they do not need controlled or summoned. They are fully fledged NPCs with drives or ideas of thier own. Stabbing and slashing weapons would not affect them.
"...the Ilthian mountains. A craggie masse of rock rysing from the Ilth'n plaines. The waters whych springe from it are ful of godeness and fortyfie those who drynk them [+1 STR]. Alas the vyle beasts resydent in these hills also bathe in these waters, and in the doing gain great strength. Foes mortallie wounded have bene known to flee, onlie to return, revytalised houres later..." - Chronicler Eamusil, Mondopedia, Vol XV (The Lands of Sylmen)