The Hanoi Imperial Citadel still carries gaping holes left by cannon fire that its north gate took in 1882. 

Bac Mon (North Gate) of the Hanoi Imperial Citadel. 

French troops fired artillery shells from warships in the Red River on April 25, 1882, leaving gaping holes in the citadel's north gate.

Bac Mon is the only gate of the citadel, built during the reign of the Nguyen Dynasty (1802-1945), that still remains standing. It can be easily spotted on Phan Dinh Phung Street.

Since Thang Long was no longer the citadel back 1805, King Gia Long of the Nguyen Dynasty built one that was much smaller than the previous Thang Long Citadel. In 1831, under the reign of King Minh Mang or the second emperor of the Nguyen Dynasty, the name was changed from Thang Long to Hanoi.

The gate has Chinese characters that mean "North Gate."

Since the old stairs were destroyed, an iron one has been built to allow visitors to go up.

On top is the reconstructed Vong Lau that keeps the ancestral tablets and statues of Nguyen Tri Phuong and Hoang Dieu, two heroes who died when fighting the French and defending Hanoi.

Their bronze statues are placed in a wooden altar.

The historical building welcome visitors from 8 a.m.-5 p.m. every day except Monday. Entry costs VND30,000 ($1.3).

The Imperial Citadel of Thang Long was regconized as a world heritage site by UNESCO in 2010.