cit·a·del /ˈsɪtədḷ, ˌdɛl/
  炮郭,根據地,大本營
  Cit·a·del n.  A fortress in or near a fortified city, commanding the city and fortifications, and intended as a final point of defense.
  Syn. -- Stronghold. See Fortress.
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  citadel
       n : a stronghold into which people could go for shelter during a
           battle [syn: bastion]