Nammun (Southgate) was the grandest and most important one out of four main gates at Namhansanseong (Namhan Mountain Fortress) and it is still the most used for entry. From prior records, it appears that the gate existed before King Injo had the fortress built in 1624. It was restored in 1779. King Injo entered the fortress through this gate when taking refuge from the Manchu invasion of 1636.