Sima Yi's "Luoshui Oath" is a controversial oath in history, however, what is less known is why Sima Yi chose to swear by Luoshui. In August 25 AD, Liu Xiu led a huge army south and besieged Luoyang. The defender of the city, Zhu Kun, resisted vigorously, leaving the Han army in a difficult situation. Liu Xiu was strong, but what bothered him was the insistence of the defenders in the city, which brought the siege to a stalemate.
In order to break the deadlock, Liu Xiu sent Cen Peng, Zhu Kun's old subordinate, to persuade him to surrender. Zhu Kun was in a predicament, and the hearts of the soldiers in the city were shaken, but he was worried about helping the first emperor Liu Xuan to kill Liu Xiu's brother Liu Xuan, and he did not dare to surrender. After Liu Xiu's death, Zhu Kun repeatedly objected to Emperor Gengshi's dispatch of Liu Xiu to send troops, which made him have a deep hatred for Liu Xiu. When Cen Peng conveyed Zhu Kun's concerns to Liu Xiu, Liu Xiu stood by Luoshui and made a memorable oath: "How can a person who does great things hold a grudge because of a small personal grudge?"If Zhu Kun has the heart to surrender, I can even keep his official title, how can I kill him?Luo Shui is here to testify, I will never break my word!”
Sure enough, when Zhu Kun surrendered, Liu Xiu kept his promise and even appointed him as General Pingdi and Marquis of Fugou. Liu Xiu's tolerance and honesty have made this "Luoshui Oath" a good story that has been passed down through the ages.