護城河
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.
古老的城堡被一條寬闊的護城河保護著。
• They had to cross the moat to enter the fortress.
他們必須穿過護城河才能進入堡壘。