居庸关
Seeing the progress of the rebels, on April 5, the Ming Chongzhen Emperor requested the urgent help of any military commandant in the empire. Eager to secure the loyalty of his military elite, on April 11 he granted the title of "earl" to four generals, including Wu Sangui and Tang Tong (唐通). Tang Tong, the only one of these new earls who was then in Beijing, reorganized the capital's defenses and, with a eunuch named Du Xun (杜勳), went to fortify Juyong Pass, the last stronghold protecting the northern approach to Beijing. On April 22, the Ming court learned that Tang Tong had surrendered to Li Zicheng the day before, and that the rebels' army was now in Changping, sixty-five kilometers northwest of Beijing.