fortification
noun uk/ˌfɔː.tɪ.fɪˈkeɪ.ʃən/ us/ˌfɔːr.t̬ə.fəˈkeɪ.ʃən/
[ C usually plural ]防御工事
strong walls, towers, etc. that are built to protect a place
Some of the old fortifications still exist. 一些古老的防御工事仍然存在。
The fortifications of the castle were massive and impenetrable. 城堡的防御工事巨大厚实，坚不可摧。
[ U ]强化；设防
the act of fortifying something