: IMO I think you are being too literal, it is doubtful that the Dwarves would dig into solid mountain, more expand (as others have suggested) a natural cave system. I also think Durin DID see the crown in the mirrormere, Gimli certainly did. Placed there as it was close to an ideal cave sytstem for a mountain fortress, not randomly.
: Not withstanding this, the dwarves would have expanded and enlarged the caverns and fissures for their own ends, and it would still require thousands of dwarves working for thousands of years 'chip by chip'. They were however I believe beautfying, functionallising and connecting as opposed to hewig out bare caverns. Where for example would they all have lived for the first few hundred years if there was no cave system?
: In terms of their food (which cropped up elsewhere - underground fungi, herds of edile mountain ox/cattle/goats etc. Crops nearby, underground lakes for fish.
: Seems to me,Aule would have put the vision of the crown near an ideal home, both cave system and edible ecolcgy, pluys defensive position etc. etc.
: IMHO
: Dave

Oh absolutely. However, the original question was how much effort would it take to create Khazad-dum. I have no idea what the exact nature of the mountains was, and so I just put together some assumptions from which we can see that even if the mountains were solid, the dwarves had plenty of time in which to carve out the vast underground kingdom. Most mountains contain fissures and caverns, very few are completely solid, but I would have to have much more detailed information to put together an accurate estimate of how many dwarves it would take. Still, I agree that while they may have done soem signifiant delving after precious ores, they probably expanded on the natural formations of the caverns, meaning that the Kingdom was always more like an open-air city rather then it starting as some mining tunnels.

-RobRoy