铜墙铁壁 tóng qiáng tiě bì

DEFINITIONS

  1. copper wall, iron bastion (idiom); impenetrable defense

CHARACTERS

铜 tóng
HSK 6
copper, brass, bronze
墙 qiáng
HSK 5
wall
铁 tiě
HSK 3
iron; strong, solid, firm
壁 bì
HSK 5
partition wall; walls of a house