One more thing, I've always thought it quite a statement that there were only
two entrances to Moria...one thru a password protected 'secret' door and
another that led to a single file only bridge. It's excellent security
against invasion. No armies could enter without ambush. Well,
almost none anyway.
The problem is, of course, the unexpected catastrophe on the inside that would
need ciy-size evacuation immediately. The Dwarves didn't design Moria as
a tomb, so there must have been hundreds of secret doors OUT - only open
from the inside - and maybe a couple that could be opened from the outside in
case of avalanche or something. Only Doriath may have been better
protected.
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