eryndel said:
I don't typically like to contradict sages, but... here goes.
Look closely at City of the Dead and you'll notice that all the undead created are mindless and uncontrolled, which doesn't work so well for creating an army. Also, the XP expenditure is sizeable, I think 3K per spellcaster (and you'd need maybe a score of spellcasters to tackle a decent sized city.)
Werner
So that means that Nightfall was wrong not once, but three times.
Yay Nightfall.
On to the topic at hand:
Raising an army of undead isn't too difficult - multiple castings of animate dead do it.
Controlling them is a different matter.
Potentially you could use illusions to move the undead to wherever you want them to fight - skeletons attack mercilessly, and presumably attack any living thing mercilessly. They're never going to be able to disbelieve an illusion that they don't get near, so leading them around with a permanent illusion would seem to fit the bill.
Alternately choosing a controlled skeleton, outfitting it with a "hat of disguise" and leading your uncontrolled skeletons around with that would presumably also work, and would be a more long-term solution.
When you want the force to stay still, you merely let the illusion lapse, or order your skeleton to stop using the hat.
This is assuming, of course, that skeletons (or zombies, or whatever) don't attack other undead.