The Flag Tower is on Dien Bien Phu Street, Ba Dinh District, Hanoi; near Ba Dinh Square. This flag tower, also called Cot Co, is one of the rare architectural works in Hanoi that was fortunate enough to not be destroyed by the French administration between 1894 and 1897. It was used by French troops as an observation tower and communication station between command headquarters and adjacent military posts.

The Hanoi Flag Tower was built in 1812 and is composed of three platforms and a tower. The words Nghenh Huc, meaning “to welcome dawn’s sunlight,” are inscribed on the eastern door. The western door bears the two words Hoi Quang, meaning “to reflect light,” and the southern door, Huong Minh, meaning “directed to the sunlight.” The tower is lightened by 36 flower-shaped and 6 fan-shaped windows. The National Flag of Vietnam is on top of the tower.