Incident at Gaoping Tombs 高平陵之變

When Emperor Ming died in the 1st month of the 3rd year of Jingchu (239) and Cao Fang, Prince of Qi, took the throne, the General-in-Chief Cao Shuang and the Grand Commandant Sima Yi assisted in the government. Cao Shuang at first served Sima Yi like a father because of his age and virtue, but following Ding Mi's plan he petitioned the Son of Heaven to transfer Sima Yi to the post of Grand Tutor. Outwardly this honored him, but inwardly it was meant to ensure that the business of the Imperial Secretariat passed through Cao Shuang first. With He Yan, Deng Yang and Ding Mi made Masters of Writing, Bi Gui Colonel-Director of Retainers and Li Sheng Intendant of Henan, matters seldom went through Sima Yi, and Sima Yi avoided Cao Shuang on the pretext of illness. Records, Wei 4 §2Records, Wei 9 §71–72 · 76

He Yan and the others divided among themselves the mulberry fields of the agricultural colonies and the bath-town estates and misappropriated government property, while Cao Shuang's food, carriages and clothing rivaled those of the Son of Heaven, and he privately took the late emperor's palace ladies to be his entertainers. His younger brother Cao Xi wrote essays and remonstrated with him many times, but was not heeded, and Sima Yi secretly made preparations. In the winter of the 9th year of Zhengshi (248), when Li Sheng, appointed Inspector of Jing Province, came to call, Sima Yi pretended to be gravely ill and showed himself feeble, and Li Sheng believed it. Records, Wei 9 §76–79

On the jiawu day of the 1st month of the 10th year of Zhengshi (1st year of Jiaping, 249), when the emperor's carriage went to pay respects at the Gaoping Tombs and Cao Shuang and his brothers all followed, Sima Yi marshaled his troops, first seized the arsenal, and stationed himself at the pontoon bridge over the Luo River. He memorialized that Cao Shuang had betrayed the late emperor's testamentary charge, imitated the Son of Heaven, and colluded with the eunuch Zhang Dang to covet the sacred vessels of state, and said that the Grand Commandant Jiang Ji, the Prefect of the Imperial Secretariat Sima Fu and others had petitioned the Yongning Palace and received the Empress Dowager's command to dismiss the troops of Cao Shuang, Cao Xi and Cao Xun and send them home to their residences as marquises. Jiang Ji followed Sima Yi and stationed himself at the pontoon bridge. The biography of Gao Rou says that the Empress Dowager summoned Gao Rou, granted him the Tally (jiajie) and had him act as General-in-Chief to take over Cao Shuang's camp, and the biography of Wang Guan records that Sima Yi had Wang Guan act as Commander of the Central Army to take over Cao Xi's camp. Records, Wei 4 §28Records, Wei 9 §80–83Records, Wei 14 §140Records, Wei 24 §57 · 78

Cao Shuang did not pass the memorial on to the Son of Heaven and did not know what to do. Huan Fan, Minister of Agriculture, ignored the Empress Dowager's summons, forged an edict to have the Pingchang Gate opened, fled south to Cao Shuang, and urged him to move the Son of Heaven to Xuchang and call up troops from outside the capital. Sima Yi said that Cao Shuang would not be able to use Huan Fan's plan, and Cao Shuang and his brothers did indeed hesitate. When the Palace Attendant Xu Yun and the Master of Writing Chen Tai persuaded Cao Shuang to confess his guilt early, Cao Shuang sent the two men to Sima Yi to confess his guilt and ask for death, and only then passed the memorial on; he and his brothers were all dismissed and returned to their residences. Records, Wei 9 §84–85

Four days later, on the wuxu day, the officials in charge arrested the eunuch Zhang Dang and interrogated him, and Zhang Dang testified that Cao Shuang had plotted rebellion with He Yan and others, had drilled troops in advance and meant to strike in the 3rd month. After deliberation at court, Cao Shuang, Cao Xi, Cao Xun, He Yan, Deng Yang, Ding Mi, Bi Gui, Li Sheng, Huan Fan, Zhang Dang and others were all executed and their clans exterminated to the third degree. Jiang Ji was made Marquis of a Chief District for this achievement, but he submitted a memorial saying that he had not known of the plan in advance and had not led the fighting. Records, Wei 4 §28Records, Wei 9 §87–88Records, Wei 14 §140

The aftermath of the incident was great. Xiahou Ba, who had been treated generously by Cao Shuang, grew suspicious of his own position on hearing that Cao Shuang had been executed and fled to Shu. Sima Yi promoted Wang Ling to Grand Commandant, but Wang Ling, together with his nephew Linghu Yu, saying that the Prince of Qi was unequal to the imperial throne, plotted to set up Cao Biao, Prince of Chu. In his assessment in the Annals of the Three Young Emperors, Chen Shou said that Emperor Ming did not entrust the affairs after his death wholly to one man but mixed in members of collateral branches, which led in the end to the extermination of Cao Shuang and the deposition of the Prince of Qi; in his assessment in the Biographies of the Various Xiahou and Cao, he said that Cao Shuang, thin in virtue and high in rank, sank into excess. Records, Wei 9 §27 · 132Records, Wei 28 §6Records, Wei 4 §152