Yu Jie

Yu Jie, as a Song general, implemented a comprehensive fortification system in Sichuan, building a network of mountain fortresses such as Diaoyu Cheng. These defenses utilized the rugged terrain to neutralize Mongol cavalry advantages. His strategy proved highly effective, stalling the Mongol advance for decades.

Yu Jie died under suspicious circumstances, with historical accounts suggesting he was poisoned on orders from the Song court. His successful fortifications had made him powerful, leading to court intrigue and accusations of disloyalty. His death weakened Sichuan's defenses and demoralized the military.