In the first month of the lunar calendar in 1370 , King Gongmin of Koryo sent Li Chenggui to lead 5,000 cavalry and 10,000 infantry. They traveled more than 600 miles from Huangcaoling in the northeast of Koryo to Xuehanling, and traveled another 700 miles. On the first month of Jiachen, they crossed the Yalu River. That night, the sky was filled with purple air in the northwest. The Koreans considered this a sign of victory. At that time, Li (Yi) Wulu Timur, the Tongzhi of Dongning Prefecture (Dongnyeong Prefectures), fled to Yuluoshan City ( Wunü Mountain City ).