bar·bi·can /ˈbɑrbɪkən/
  外堡;望樓;城門塔
  Bar·bi·can Bar·ba·can  n.
  1. Fort. A tower or advanced work defending the entrance to a castle or city, as at a gate or bridge. It was often large and strong, having a ditch and drawbridge of its own.
  2. An opening in the wall of a fortress, through which missiles were discharged upon an enemy.
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  barbican
       n : a tower that is part of a defensive structure (such as a
           castle) [syn: barbacan]