Biography
Family Background and Early Life
Li Su was born into one of the most distinguished military families of the mid-Tang period. His father, Li Sheng, was a renowned general of the restoration era who helped suppress the rebellion of Zhu Ci and recover Chang'an. For these achievements he was enfeoffed as Prince of Xiping Commandery and had his portrait placed in Lingyan Pavilion during Emperor Dezong's reign. Li Sheng had fifteen sons, of whom Li Su was the eleventh. Li Su's birth mother died early, and he was raised by Lady Wang, Duchess of Jin. When Lady Wang died, Li Sheng ordered Li Su to wear only the mourning dress prescribed for a more distant relation because she was not his birth mother. Li Su wept bitterly and insisted on observing the heavier mourning dress appropriate to a mother. Moved by his filial devotion, Li Sheng agreed. The *Old Book of Tang* records: “Su lost his birth mother early and was raised by Lady Wang, Duchess of Jin. When she died, Sheng, because she was not his principal wife, ordered him to wear the sima mourning dress. He cried and could not bear it; Sheng was moved and permitted him to wear the heavier mourning.” The episode was later cited as evidence of Li Su's filial devotion, strong temperament, and deep sense of personal loyalty.
Li Su entered official service through hereditary privilege and was first appointed Pitch Regulator of the Court of Imperial Sacrifices, later becoming Vice Director of the Court of Imperial Guards. In 793, the ninth year of Zhenyuan, Li Sheng died. Li Su and his elder brother Li Xian built a hut beside the tomb and observed mourning there. Emperor Dezong feared that their grief would damage their health and ordered them to return home. Li Su obeyed, spent one night at home, and then ran barefoot back to the tomb. Recognizing that his resolve could not be changed, Dezong allowed him to complete the full three-year mourning period. Contemporaries praised the episode, and it accorded with the style of sincere treatment and moral obligation that later characterized Li Su's relations with his soldiers.
Middle Career
After completing mourning, Li Su was appointed Right Junior Preceptor of the Heir Apparent. He later served as Director of the Court of the Imperial Treasury and Left Junior Preceptor of the Heir Apparent, and was sent out as prefect of Fang and Jin prefectures. His local administration was regarded as effective, and he received the rank of Grand Master for Splendid Happiness after strong performance evaluations. He later returned to court, again served in the heir apparent's establishment, and rose to Supervisor of the Household of the Crown Prince and Commissioner of Palace Gardens and Stables.
Li Su's middle career was steady but lacked major military accomplishments. Although he was a capable strategist and skilled horseman and archer, he spent many years in offices attached to the Eastern Palace or as a prefect and had few opportunities to demonstrate military ability. The relatively quiet period nevertheless tempered his character and deepened his understanding of the dangers posed by semi-independent regional military governments.
Commission to Suppress the Rebellion
In 814, the ninth year of Yuanhe, Wu Shaoyang, military commissioner of Huaixi, died. His son Wu Yuanji seized control of the army without authorization, and Emperor Xianzong of Tang resolved to suppress him by force. The war dragged on. In 816, the eleventh year of Yuanhe, Gao Xiayu, military commissioner of Tang and Deng, suffered a severe defeat at Tiecheng, and his successor Yuan Zi likewise failed to make progress after prolonged fighting. Tang morale on the western front collapsed, and the campaign against Huaixi reached a stalemate.
Li Su then submitted a memorial volunteering for frontline service. Chancellor Li Fengji also appreciated his abilities. In the twelfth lunar month of 816, Li Su was appointed Left Cavalier Attendant-in-Ordinary, concurrently prefect of Deng Prefecture and Censor-in-chief, and military commissioner of Sui, Tang, and Deng prefectures, replacing Yuan Zi and taking command of the western front.
After arriving, Li Su did not immediately tighten discipline or prepare for battle. He knew that the Tang forces had just been defeated and were demoralized, while the rebels had grown arrogant after repeatedly defeating Gao and Yuan. He therefore deliberately presented an appearance of weakness, refrained from imposing strict discipline, and told his soldiers: “The Son of Heaven knows that I am compassionate and can endure humiliation, and therefore ordered me to care for you. Fighting is not my business.” He dismissed female entertainers, held no banquets, and personally comforted wounded and sick troops. Because Li Su previously held no great military reputation and appeared to have no intention of preparing for battle, the rebels relaxed their vigilance and stopped strengthening their defenses.
Preparing the Huaixi Campaign
While presenting weakness outwardly, Li Su secretly planned a direct strike on Cai Prefecture. He treated surrendering soldiers generously and personally questioned every Huaixi deserter, gradually gaining detailed knowledge of enemy terrain, troop deployments, and weaknesses. In the second lunar month of 817, a patrol commanded by Ma Shaoliang captured Wu Yuanji's fierce general Ding Shiliang. Li Su's officers urged that Ding be executed, but Li Su saw that he showed no fear and praised him as “a true man,” personally releasing him from his bonds. Ding Shiliang was moved to tears and vowed to repay him with his life. He then proposed a plan that led to the capture of Chen Guangqia, principal adviser to Wu Xiulin, commander of Wencheng Stockade. In the third lunar month, Wu Xiulin surrendered with three thousand men. Li Su patted him on the back in reassurance, incorporated his troops, and employed his brave subordinate Li Xian, changing the man's name to Li Zhongyi.
Li Su asked Wu Xiulin how Cai Prefecture might be taken. Wu replied that victory required Li You, a brave and capable Huaixi cavalry commander who held Xingqiao Stockade and had repeatedly defeated government troops. Li Su arranged an ambush by sending Shi Yongcheng with three hundred cavalry to lure Li You into pursuit and capture him. Because Li You had killed and wounded many Tang soldiers, the army clamored for his execution. Li Su overruled them, released Li You from bonds, and treated him as an honored guest. Li Su held private discussions with Li You and Li Zhongyi, often until midnight, which made other officers suspect that Li You was secretly working for the enemy. Under pressure from the army, Li Su sent Li You in chains to the capital while secretly memorializing Emperor Xianzong: “If Li You is killed, there will be no way to achieve success.” Xianzong ordered Li You released. Li Su was delighted and appointed him commissioner of detached troops, later making him Commissioner of the Six Garrisons with command of three thousand elite troops of Shannan East Circuit. Grateful for Li Su's trust, Li You served with complete loyalty and became a key planner of the assault on Cai Prefecture.
Snowy-Night Attack on Cai Prefecture
In the ninth lunar month of 817, the twelfth year of Yuanhe, Li Su judged the time ripe and secretly submitted his plan for a surprise attack on Cai Prefecture to Chancellor Pei Du. Pei strongly approved and authorized the operation. On the tenth day of the tenth lunar month, amid wind and snow, Li Su sent three thousand men as the vanguard, personally led another three thousand in the center, and placed three thousand more in the rear. The army moved east in secrecy. The initial order merely instructed the troops to march sixty *li* east and capture Zhangchai Village, a strategic point about seventy *li* from Cai Prefecture. After taking the village and allowing a brief rest, Li Su revealed that the true objective was Cai Prefecture. His officers were terrified; even the army supervisor wept, believing that Li You had deceived them. The snowstorm tore the banners, men and horses froze to death along the road, and many soldiers believed they would not survive.
The Tang army forced a march of thirty-five kilometers and reached the walls of Cai Prefecture. Near the city was a pond filled with chickens and ducks. Li Su ordered his soldiers to disturb the birds so that their cries would mask the sound of the advancing army. Since Wu Shaoyang had first defied the court, no government army had reached the walls of Cai Prefecture for thirty years. Combined with the heavy snow, this left the defenders completely unprepared. Li Su and his officers led from the front, cut footholds into the city wall, climbed first, and killed sleeping guards, while leaving the night watchmen to continue sounding the watches as usual. Wu Yuanji initially refused to believe that government troops had entered the city and assumed that prisoners were rioting. When he finally confirmed the truth, he was shocked, withdrew with his attendants into the headquarters citadel, and sent men to Huiqu for aid.
After entering the city, Li Su treated the family of Dong Chongzhi, commander at Huiqu, with generosity and sent Dong's son to summon him to surrender. Meanwhile, Li Su intensified the attack on the citadel. Wu Yuanji had lost local support, and townspeople competed to help the Tang troops carry firewood to burn the gates. On the twelfth day of the tenth lunar month, the citadel fell. Wu Yuanji surrendered and was transported to the capital in a cage. More than twenty thousand troops in Shen and Guang prefectures surrendered at the same time. The Huaixi Rebellion was ended.
Later Years
After the pacification of Huaixi, Li Su was appointed Acting Left Vice Director of the Department of State Affairs, concurrently military commissioner of Shannan East Circuit, and enfeoffed as Duke of Liang. In 818, the thirteenth year of Yuanhe, he was transferred as Military Commissioner of Wuning and joined the campaign against the rebellious Pinglu military governor Li Shidao. At Jinxiang, Li Su inflicted a major defeat on Li Shidao's army and won repeated engagements, contributing to the suppression of the Ziqing rebellion.
In 820, the fifteenth year of Yuanhe, Emperor Xianzong died and Emperor Muzong succeeded. Li Su was appointed Chancellor with the designation Tong Pingzhangshi and military commissioner of Zhaoyi, and soon afterward was transferred to Weibo. In 821, the first year of Changqing, Tian Hongzheng, military commissioner of Chengde, was killed. Li Su wanted to raise troops to avenge him, but serious illness prevented him from doing so. He returned to Luoyang to recover and was appointed Junior Guardian of the Crown Prince. He died in the tenth lunar month of the same year at the age of forty-nine. The court posthumously granted him the office of Defender-in-chief and the posthumous name Wu. In 846, the sixth year of Huichang, he was granted sacrificial association in the Temple of King Wucheng.