堀
a deep, wide ditch surrounding a castle, fort, or town, typically filled with water and intended as a defense against attack
:
• The ancient castle was protected by a wide moat.
その古い城は広い堀で守られていた。
• They had to cross the moat to enter the fortress.
彼らは要塞に入るために堀を渡らなければならなかった。