Chinese idiom · 成语
固若金汤
Meaning
As secure as metal walls and a boiling moat; exceptionally difficult to breach.
Character by character
Origin and story
Historical metaphorThe underlying image is a metal-walled city with a moat of boiling water: defenses so forbidding that an attacker cannot break through. In the Book of Han's biography of Kuai Tong, the adviser warns Wu Chen that killing a magistrate who surrenders would make other cities resist desperately. They would effectively become such impregnable fortresses. Rewarding the first surrender, he argues, would instead encourage others to follow.
The passage uses jin cheng tang chi, not the exact modern phrase. Gu ruo jin tang draws on that image to describe exceptionally secure defenses. Tang means hot or boiling water here, not soup or broth.
Sources and further reading
In everyday life
对手的防守固若金汤，我们整场比赛都没找到突破口。
The opposing defense was impregnable; we never found an opening throughout the match.
A strong metaphor for tight defense, including in sports.