n. 外堡, 碉楼

[ noun ]
a tower that is part of a defensive structure (such as a castle)
<noun.artifact>

Barbican \Bar"bi*can\, Barbacan \Bar"ba*can\, n. [OE. barbican,
barbecan, F. barbacane, LL. barbacana, barbicana, of
uncertain origin: cf. Ar. barbakh aqueduct, sewer. F.
barbacane also means, an opening to let out water, loophole.]
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.