The turning point of Li Shih-min's campaign in 621 A.D. against the two rebels, Tou Chien-te, King of Hsia, and Wang Shih-ch`ung, Prince of Cheng, was his seizure of the heights of Wu-lao, in spike of which Tou Chien-te persisted in his attempt to relieve his ally in Lo-yang, was defeated and taken prisoner. See CHIU T`ANG, ch. 2, fol. 5 verso, and also ch. 54.