In the final years of the Qin Dynasty, Chen Sheng and Wu Guang raised the banner of rebellion at Daze Township, swiftly capturing key positions and establishing the Zhang Chu regime. Chen Sheng then ordered the general Wu Chen, styled Lord Wuxin, to lead an army against the Yan and Zhao territories. Wu Chen's first target was the city of Fanyang.
At this time, a man named Kuai Tong arrived at the Fanyang county office seeking an audience with Magistrate Xu Gong, who received him.
Kuai Tong said to Lord Xu, "I am a commoner from this county, named Kuai Tong. I know you are about to die, so I have come especially to offer condolences. However, I must also congratulate you, for today you have received me, and I can grant you a new life."
Xu Gong, puzzled by Kuai Tong's words, replied, "Sir, your words are too cryptic. I don't understand what you mean."
Kuai Tong laughed heartily and said, "Master Xu, you have been the magistrate of Fanyang for over a decade, and countless people have suffered under your brutal torture, even to the point of death. Their families and they themselves have long sought revenge against you. Only because the Qin laws were so harsh did they dare not act against you. But now the world is in chaos; King Chen has sent General Wu Xin to march on Fanyang. If the townspeople seize this chance to retaliate, your head will be lost. That is why I have come early to offer my condolences!"
Duke Xu nodded and said, "Sir, what you say makes sense. The situation is indeed grave now. So what is your method to give me a new lease on life?"
Kuai Tong, brimming with confidence, declared, "Though I am not a man of great learning, I have heard that Lord Wu Xin respects the worthy and treats his subordinates with courtesy. He will surely send someone to seek my advice on the strategy for pacifying Yan and Zhao. I plan to tell him this: 'Conquering cities and territories through bloody warfare is not a wise approach. If you adopt my plan, you can pacify a thousand li of land without losing a single soldier—just by issuing a single proclamation. Now, Magistrate Xu of Fanyang is ready to surrender his city to you. If you refuse his submission and kill him, then every defender in Yan and Zhao will know that surrendering means death, and they will defend their cities to the last. Their walls will become as strong as cast metal, and their moats as impassable as boiling water—your army will never breach them. In my view, you should accept Xu's surrender, reward him generously, and let him ride in a splendid carriage to parade through Yan and Zhao. When the defenders there see that Xu gained even greater wealth and honor after surrendering, they will rush to submit to you. Then, with just one proclamation, you can pacify a thousand li of land.'"
After hearing Kuai Tong's words, Duke Xu said, "You are absolutely right. You have enlightened me completely. Thank you so much!"
So Lord Xu immediately sent Kuai Tong by carriage to meet Lord Wuxin. After hearing Kuai Tong's words, Lord Wuxin promptly adopted his strategy, dispatched a massive convoy, accepted Lord Xu's surrender, and bestowed generous rewards upon him.
Soon, the news spread like wildfire across the lands of Yan and Zhao, prompting over thirty city commanders to surrender one after another. As a result, Lord Wu Xin swiftly pacified the entire region of Yan and Zhao.
Later, the idiom "Golden City and Soup Moat" came to describe a city or fortress that is extremely well-defended.
Source: *Book of Han*, "Biography of Kuai Tong"
Meaning of the Idiom: Later, the Chinese idiom "金城汤池" came to describe a city or fortress that is extremely well-defended.