Located just inside the Citadel ramparts, near the gates to either side of the Flag Tower, are the Nine Holy Cannons (1804), symbolic protectors of the palace and kingdom. Commissioned by Emperor Gia Long, they were never intended to be fired. The four cannons near Ngan Gate represent the four seasons, while the five cannons next to Quang Duc Gate represent the five elements: metal, wood, water, fire and earth.
Each brass cannon is 5m long and weighs about 10 tonnes.