castle wall; rampart; defensive wall
Refers to the thick outer walls of a castle or fortified town, often made of stone or earth. Can also be used for city walls in historical contexts.
The castle walls are as high as 10 meters.
The town was surrounded by tall castle walls.
Medieval towns were surrounded by defensive walls.
The king built a castle wall to keep out invaders.
Part of the old castle wall collapsed in the earthquake.
The enemy army finally breached the castle wall and stormed inside.
塀 is a general, everyday word for a fence or wall around a house or yard, while 城壁 specifically denotes the massive defensive wall of a castle or fortified town.
城壁 refers specifically to the defensive wall itself, while 城郭 can mean either the whole fortified complex or its walls, making the two easy to mix up in narrower contexts.
Compound of 城 (castle) and 壁 (wall). The reading is on'yomi, reflecting its Sino-Japanese origin.