bar·bi·can 
(bärbĭ-kən)
(bärbĭ-kən)n.
A tower or other fortification on the approach to a castle or town, especially one at a gate or drawbridge.
[Middle English, from Old French barbacane, from Medieval Latin barbacana, from Persian barbārkhān : barbār, guard (from Old Iranian *parivāraka-, protective; see wer-4 in the Appendix of Indo-European roots) + khān, house (from Middle Persian).]