The Chi Lang Border is located in Chi Lang District, Lang Son Province. The defile consists of a valley surrounded by high mountains and through which runs the Thuong River.

The mountains were opened in two locations to form two gates. The northern gate was named Quy Mon Quan, meaning "monster gate," after the Chinese invaders who entered Vietnam through this gate. The southern gate was called Ngo The, meaning "swearing gate." Vietnamese ancestors who swore to sacrifice their lives to protect their motherland and to prevent invaders from entering Vietnam via this defile built the gates.

In the past, in this area that King Le Hoan defeated the Chinese Sung troops in 981 and killed all the enemies. In 1076, Prince Consort Than Canh Phuc set a front line against 300,000 Sung enemies. Led by Quach Quy in 1285, Nguyen Dia Lo killed traitor Tran Kien in the second National Resistance against Yuan-Mongol invaders. In 1427, Lam Son righteous army killed invader leader Lieu Thang, caught Hoang Phuc, killed 10,000 Ming enemies and overthrew all their maneuvers.

Now Chi Lang Defile is considered a historical vestige with imposing landscape where visitors stop to enjoy the natural scenery.