Princess Taihe (太和公主, personal name unknown), later known as Princess Ding'an (定安公主) or Princess Anding (安定公主), was a princess of the Chinese Tang Dynasty and a Khatun (empress) of Huigu. She was married to Huige's Chongde Khan as part of the Heqin system of marriages between Tang princesses and Huigu khans, but suffered through Huigu's subsequent collapse before being welcomed back to the Tang court. Background and entry into marriage It is not known when Princess Taihe was born, although it is known that she was a daughter of Emperor Xianzong (r. 805–820) and Emperor Xianzong's wife Consort Guo, and that she was younger than her full brother Li Heng, who was born in 795. She was Emperor Xianzong's 10th daughter over all. Late in Emperor Xianzong's reign, Huigu, then reigned by Baoyi Khan, made repeated overtures to request a Tang princess to be married to Baoyi Khan under the Heqin system. Eventually, after a mission headed by the Huigu diplomat Hedagan (合達干), Emperor Muzong agreed to have Princess Taihe's older sister Princess Yong'an married to Baoyi Khan — but as Baoyi died in 821, the marriage never took place. After Baoyi Khan died in 821 and was succeeded by Chongde Khan, Chongde Khan continued to seek marriage with a Tang princess, and he sent a delegation including a number of officials and two Huigu princesses, along with a bride price of horses and camels. Later in 821, Li Heng, who was by now emperor (as Emperor Muzong), agreed to marry Princess Taihe to Chongde Khan. When another neighbor state, Tufan, became aware of the Tang-Huigu marriage, it was incensed and attacked Fort Qingsai (青塞堡, in modern Yulin, Shaanxi), but the Tufan attack was repelled. On August 28, she departed the Tang capital Chang'an, escorted by the general Hu Zheng (胡証), assisted by the other officials Li Xian (李憲) and Yin You (殷侑). Anticipating a possible attempt to Tufan forces to intercept Princess Taihe's train, Huigu forces were dispatched to escort them as well as to attack Tufan's borders. Emperor Muzong issued an edict permitting Princess Taihe to maintain a staff on the same level of staffing as an imperial prince. Princess Taihe's train did not arrive at the Huigu court until late 822. When they approached the Huigu court, Chongde Khan sent a group of several hundred soldiers to welcome her and escort her to the Huigu court, but