原: 武信君 蒯通傳, 史記, 後漢書 等等
金城湯池 (금성탕지,jīnchéng tāngchí,きんじょうとうち), metal fortress boiling pond
A word to refer to an impregnable place or thing

Emperor Si-hwang (始皇帝) of Jin (秦) had unified the kingdoms, but it started to decline soon after his death. The families (宗室) and those who had served (遺臣) in old kingdoms rose up to overthrow Jin. Many claimed to be a king in their own right, and the governing system of Jin (郡縣制) was being dismantled completely. It was during this time a man named Mu-sin (武信) had subdued the old territory of Jo (趙) and people called him Lord Mu-sin (武信君). Koi-tong (蒯通), an unappointed advisor (論客), saw all this take place, and told Seo-gong (徐公), a ruler (縣令) of Beom-yang (范陽), that the disgruntled people under his rule are about to rise up against him. Seo-gong asked what Koi-tong had in mind, and Koi-tong said that he will go to Lord Mu-sin and convince him that he should make a good example of how someone who surrenders to him would be treated by accepting your surrender, and treating you with extremely generosity. The logic was that if Seo-gong surrendered and he was treated poorly, other fortresses with become even more impregnable (金城湯池) in defending their places. So, that way, Lord Mu-sin will not suffer loss of war, and others will see how you were treated, and instead of suffering great losses themselves, they will find that it’s better to surrender. Seo-gong sent Koi-tong to Lord Mu-shin.  Lord-Mushin, amazed at the wisdom of Koi-tong, invited Seo-gong with the utmost respect and had him go abroad to tell people of this. People of Beom-yang was spared from a war, so they praised Seo-gong, and other regions hearing of this also surrendered to Lord Mu-sin.  It is said that over 30 fortresses had surrendered in the region of Hwa-buk (華北) alone.