铜墙铁壁 (銅牆鐵壁) tóng qiáng tiě bì

tóng qiáng tiě bì set phrase copper wall, iron bastion; impenetrable defense
Domain: Idiom 成语
Notes: (CC-CEDICT '銅牆鐵壁'; Guoyu '銅牆鐵壁')