铜墙铁壁

Traditional form:

銅牆鐵壁

Pinyin (reading):

tóngqiángtiěbì

Definitions:

• copper wall, iron bastion (idiom); impenetrable defense

Characters:

• 铜 - copper, bronze
• 墙 - wall
• 铁 - iron; strong, solid, firm
• 壁 - partition, wall; rampart

Traditional characters:

• 銅 - copper, bronze
• 牆 - wall
• 鐵 - iron; strong, solid, firm
• 壁 - partition, wall; rampart