The king, along with 13,800 soldiers, took refuge at the Namhan Mountain Fortress, which did not have enough provisions stockpiled for such a large number of people. Hong Taiji's main division, 70,000 strong laid siege to the fortress. Provincial forces from around the country began moving in to relieve Injo and his small retinue of defenders. Forces under Hong Myeonggu and Yu Lim, 5,000 strong, engaged 6,000 Manchus on 28 January. The Manchu cavalry attempted frontal assaults several times but were turned back by heavy musket fire. Eventually they circumnavigated a mountain and ambushed Hong's troops from the rear, defeating them. Protected by the mountainous terrain, Yu's forces fared better and successfully decimated the Manchu forces after defeating their attacks several times throughout the day. The Joseon troops within the fortress, which consisted of both capital and prefectural armies, also successfully defended the fortress against Manchu assaults, forcing their actions to be relegated to small-scale clashes for a few weeks.