fort       
noun [ C ] uk/fɔːt/ us/fɔːrt/
 堡垒;城堡;要塞
a military building designed to be defended from attack, consisting of an area surrounded by a strong wall, in which soldiers are based
  The remains of the Roman fort are well preserved. 这个罗马要塞的遗址保存完好。 
 Synonym: fortress