This essay is an attempt to reassess the role played by Wu San-kuei during the crucial year of 1644.1 Traditionally ignored by historians or relegated to a minor role, the conventional wisdom has instead preserved the following now well established account of Wu's place in the Manchu conquest of China. When the rebel Li Tzu-ch'eng was marching eastward and advancing toward Peking, Emperor Ch'ung chen finally realized the danger of the threat. In early April he conferred upon Wu San-kuei and other able generals the title of earl; Wu was designated P'ing-hsi po (Earl who Pacified the West). The emperor further ordered Wu both to abandon the land east of the Shan-hai pass and to move the troops back to Peking to meet the threat posed by Li's advance toward Peking. Nevertheless, Wu temporarily ignored the order and delayed his march. When his troops eventually marched halfway to Feng-jun, on the 26th of April, Peking had already fallen into the hands of the rebels. Consequently, he marched back to the Shan-hai-kuan, a vital strategic town located at a pass at the east end of the Great Wall, to contemplate the next move. Meanwhile, Li Tzu-ch'eng sent a delegate to demand Wu's surrender, holding his father, the retired commander Wu Hsiang, as hostage. Wu considered complying with the demand but changed his mind upon learning that his favorite concubine, Ch'en Yüan-yüan, had also been seized. Outraged, he surrendered to the Manchus and invited them to suppress the rebellion.