Extremely solid and unbreakable; impregnable; invulnerable. It can also refer to a deeply entrenched idea, habit, or relationship that is difficult to change or destroy.
Era:
Ancient
Frequency:
Story:
During the Eastern Jin Dynasty, Fu Jian, the King of Former Qin in the north, launched an invasion against the Eastern Jin. General Zhu Xu was tasked with defending Xiangyang.
The Former Qin army besieged Xiangyang tightly, making it impossible for anyone to enter or leave.
Zhu Xu's mother, Lady Han, ascended the city wall to survey the land. She then organized women to construct a new inner city wall.
This new city was built with such exceptional strength that it was impregnable. Fu Jian's forces found themselves utterly helpless against this new, unbreakable defense.