The Gaoping Tombs Coup (高平陵之变) occurred in 249 when Cao Fang and Cao Shuang left Luoyang to pay respects at the Gaoping tombs (the tomb of Cao Rui or a related site). Sima Yi, who had feigned illness and withdrawal from politics, staged a coup. He occupied the capital, closed the gates, and declared that Cao Shuang had betrayed the trust of the late emperor. He secured the support of the empress dowager and of officials who resented Cao Shuang. When Cao Shuang heard the news, he hesitated; he was promised that he would only lose his military power if he surrendered. He surrendered and was then arrested with his brothers and allies (He Yan, Deng Yang, Li Sheng, and others). Sima Yi had them all executed with their clans. From then on, the Wei court was controlled by the Sima family. Cao Fang remained emperor in name until 254, when Sima Shi deposed him in the Gaopingling Incident.
Context
Cao Rui had entrusted Cao Fang to Cao Shuang and Sima Yi. Cao Shuang had monopolised power and sidelined Sima Yi. Sima Yi bided his time and struck when the emperor and regent were away. The coup is a classic example of a retired strongman seizing the capital in the sovereign’s absence.