The Citadel began to be built in the early 19th century. The Citadel was originally built of earth, but during the first decades of the 19th century, tens of thousands of people laboured to erect ramparts built in the style of the French military engineer Vauban. Inside the Citadel is the Imperial City, a kind of replica of Beijing's Forbidden City.
During the war with the United States, the Citadel and the Imperial City were badly damaged and only about twenty of the one and a half hundred buildings survived. Some reconstruction and restoration of the buildings is underway, but much remains in ruins.
The Ngomon Gate leads inside the Citadel and has five entrances: a central one for the Emperor, two for the royal elephants, and two more for the royal mandarin servants. The gate is crowned by the huge Watchtower of the Five Phoenixes. This is where the last emperor of the Nguyen dynasty signed his abdication in 1945.
The Cô Co signal tower rises above the southern fortifications of the Citadel. Not far from it and Ngan Gate is a parade square with nine bronze cannons - the so-called dynastic cannons. They symbolise the four seasons and the five ritual elements.
