Location: These nine holy cannons are housed in two buildings beside the The Nhan and Quang Duc Miradors in the Citadel of Hue. Characteristic: Each cannon is 5.10m long and weights more than 10 tons. Their barrels are elaborately inscribed with the titles, position order, weight, instructions, and writings on fights against the Tay Son Dynasty.

On January 1st 1803, Emperor Gia Long ordered all bronze wares of the Tay Son Dynasty to melt into nine cannons. The work was completed at the end of January 1804. The cannons were named after the four seasons and the five elements: Metal, Wood, Water, Fire, and Earth. They are the "Holy Invincible Generals". 

Originally, they were positioned in front of the Ngo Mon Gate, at the foot of the Royal Citadel wall, but later on, they were moved by order of Emperor Khai Dinh to the present-day location. The cannons have never been used for military purposes and just play a symbolic role as guardian spirits for the Citadel.