be secure against assault;impregnable; indestructible; invulnerable; solid;unbreakable; unshakable; indomitable ❍ 人民大众成了～的铜墙铁壁。The broad masses of the people became an impregnable wall of bronze. ❍ 人民武装力量，在革命战争的烈火中成长壮大，已成为一支～的人民军队。The people’s armed forces have grown and expanded amidst the flames of revolutionary war and become an indestructible people’s army.
坚不可摧
indestructible;unvulnerable
坚不可摧jiān bù kě cuī
十分坚固，难以摧毁。imdestructible, indomitable, be secure against assault, unbreakable