在护城河英文是"on the moat"。
护城河（moat）是一种古老的防御工事，最初用来保护城堡和城市免受攻击。它通常是一道挖掘在城市周围的水渠，用来阻挡敌人的进攻。
下面是一些例句：
The castle was protected by a deep moat. 城堡有一条深深的护城河保护。
The moat surrounding the city walls made it difficult for the enemy to attack. 围绕城墙的护城河使敌人难以进攻。
The moat was filled with alpgators to prevent intruders from crossing. 护城河里面有鳄鱼，防止入侵者穿过。