The royal Citadel of Hue complex has the characteristic of many strongholds and fortresses. Gia Long Emperor had it constructed in 1804, originally in earth, but additionally covered in brick later in the early 19th century.
Surrounded by a wide zigzag moat, the first layer of the royal Citadel is the defensive wall fort of 10 kilometer long, 7 meters high and 21 meters thick. The fort itself has 10 gates for pedestrians and 2 gates for water routes. Within, it also encompasses two other monarchal areas. The Imperial Enclosure, or Dai Noi, is encircled within a wall of 2.5 km long and 6 m wide. The Forbidden Purple City, within a perimeter of 1.3 km, was the reserved place for the private life of the kings and the royal members only.
Inside the complex, there is also a large cluster of smaller constructions. All of them lie around the main axis of the complex, running from north to south. Beginning with the northernmost Flag Tower, followed by the Ngo Mon (Noon) Gate, which was only reserved as a path only for the royal, and some others that show significant architectural value. Entering the Ngo Mon Gate, one will see the Belvedere of Five Phoenixes, also constructed by Emperor Gia Long in 1823 as a pavilion to list the names of successful scholars in the past. Another remarkable building is Thai Hoa Palace or the Palace of Supreme Harmony, built 1833, and used as the reception hall and the throne room of the emperor.
