Battle of Tianmenling

The Battle of Cheonmun-ryeong (Hangul: 천문령 전투), also known as the Battle of Tianmenling (Traditional Chinese: 天門嶺之戰) was a battle fought between Dae Jo-yeong, later founder of Balhae, and Li Kaigu (李楷固) a Khitan commander of Chinese Tang Dynasty.

After the fall of Goguryeo to the Silla-Tang armies, Dae Jo-yeong, along with his father Dae Jung-sang, were forced to move over into the Yingzhou province of the Tang Dynasty. In the confusion of the Khitan uprising (led by Li Jinzhong and Sun Wanrong) against the Tang in May 696, Dae Jung-sang and the Baishan Mohe leader Geolsa Biu sought independence from Tang. In spite of Empress Wu Zetian's appeasement policy, they fled eastward to the former land of Goguryeo.

The Tang sent general Li Kaigu to give chase, and subsequently Geolsa Biu and Dae Jung-sang were killed. Dae Jo-yeong integrated the Goguryeo people under the two leaders and resisted the Tang's attack. He scored a victory over the Tang at the Battle of Tianmenling, which enabled him to establish his own kingdom. He claimed himself the King of Jin in 699 and put his capital at Dongmo Mountain in the south of today's Jilin province.