Tian Chengsi (705 – March 4, 779),[1] formally the Prince of Yanmen, was a Chinese military general, monarch, and politician.
His family was from Ping Prefecture (平州, roughly modern Qinhuangdao, Hebei), and his ancestors, for several generations, had served in the military.
Late in the reign of Emperor Zhongzong's nephew Emperor Xuanzong, Tian Chengsi served as a forward commanding officer under the general An Lushan, the military governor (jiedushi) of Fanyang Circuit (范陽, headquartered in modern Beijing), and particularly impressed An with his ability to maintain strict military discipline.
An Lushan rebelled against Emperor Xuanzong's rule in late 755 and, on his campaign south to attack the Tang eastern capital Luoyang, had Tian, along with An Zhongzhi and Zhang Xiaozhong, serve as his forward commanders.
In 757, after An Lushan had been assassinated and succeeded by his son An Qingxu, Tian continued to serve under An Qingxu and commanded a campaign to capture the key Tang city of Nanyang (南陽, in modern Nanyang, Henan) and then to attack south further, but while he trapped the Tang commander Lu Jiong (魯炅) in Nanyang, he was not able to capture the city quickly, and after Lu eventually fought his way out of the siege and fled to Xiangyang, Tian abandoned the campaign as well and returned to Luoyang.
In fall 757, a joint Tang and Huige army commanded by Li Chu the Prince of Chu (the son of Emperor Xuanzong's son and successor Emperor Suzong recaptured Chang'an, forcing An Qingxu to flee north of the Yellow River.
The Tang imperial government was unsure as to what to do with the main Yan generals who surrendered and feared that removing them would lead to another rebellion.
In Tian's case, he was given five prefectures, which were made into Weibo Circuit (魏博, headquartered in modern Handan, Hebei).
Emperor Daizong sent an eunuch messenger, Sun Zhigu (孫知古), to Weibo to persuade Tian to destroy the temple.
When Tian did, Emperor Daizong rewarded him with the honorary chancellor title of Tong Zhongshu Menxia Pingzhangshi (同中書門下平章事), and also created him the Prince of Yanmen.
During the campaign, however, Tian also lost Ying Prefecture (瀛洲, in modern Cangzhou as well) to Zhu Tao.
When he died in 779, at his request and the urging of Li Baochen's, Emperor Daizong allowed Tian Yue to inherit his post, as the military governor of Weibo.