"Ai Chi Lang relic site is located about 150km from Hanoi city, in Chi Lang district. In the past, this place was the gate of Khau On town, Lang Son and marked many historical battles, preserving many victories. Today, the pass is 20km long, 3km wide and is the connecting point between the two districts of Chi Lang and Huu Lung of Lang Son. With a massive scale and rugged terrain, Ai Chi Lang is considered a wall to protect Thang Long from the invasions of the Northern invaders. The battles at Ai Chi Lang demonstrated the strategy and wisdom of his father in the defense of the country."