城壁

例句：

1. 1. The ancient city wall still stands as a testament to its history.
   古老的城墙依然矗立着，见证着它的历史。
2. 2. The fortress was built to protect the city from invaders.
   这座堡垒是为了保护城市免受侵略者的侵袭而建造的。
3. 3. The city walls were constructed during the Roman Empire.
   罗马时期的城墙是建造的。