The Imperial City (Vietnamese: Hoàng thành; chữ Hán: 皇城) is a walled enclosure within the citadel (Kinh thành; chữ Hán: 京城) of the city of Huế, the former imperial capital of Vietnam during the Nguyễn dynasty. It contains the palaces that housed the imperial family, as well as shrines, gardens, and villas for mandarins. Constructed in 1803 under Emperor Gia Long as a new capital, it mostly served a ceremonial function during the French colonial period. After the end of the monarchy in 1945, it suffered heavy damage and neglect during the Indochina Wars through the 1980s. The Imperial City was designated as a UNESCO World Heritage Site in 1993 as part of The Complex of Huế Monuments and is undergoing restoration.

In June 1802, after more than a century of division and the defeat of the Tây Sơn dynasty, Nguyễn Ánh ascended the throne of a unified Vietnam and proclaimed himself Emperor Gia Long. With a nation now stretching from the Red River Delta to the Mekong Delta, Emperor Gia Long moved the capital from the northern Thăng Long (current Hanoi) to Huế, the ancestral seat of the Nguyễn lords. Gia Long looked to "Confucianism and Chinese models of statecraft" as the best modes of authority, and with this ideology, he ordered the construction of a palace complex based on Beijing's Forbidden City in Huế. Geomancers were consulted as to a propitious location site for the new city, and construction began in 1803. Thousands of workers were ordered to build the walled citadel and ringing moat, measuring some 10 kilometres (6.2 mi) long. The original earthwork was later reinforced and faced with brick and stone resulting in 2 m (6 ft 7 in)-thick ramparts.

The citadel was oriented to face the Hương River (Perfume River) to the southeast. This differs from Beijing's Forbidden City, which faces true south. Rather than concentric rings centered on the emperor's palace, the imperial residence itself is offset toward the southeast side of the citadel, nearer the river. A second set of tall walls and a second moat were constructed around this Imperial City, within which many edifices were added in a series of gated courtyards, gardens, pavilions and palaces. The entire complex was the seat of power until the imposition of the French protectorate in the 1880s. Thereafter it existed mostly to carry on symbolic traditions until the Nguyễn dynasty was ousted in 1945, with the Proclamation of Independence of the Democratic Republic of Vietnam. The abdication ceremony of Emperor Bảo Đại took place at the Imperial City on 30 August 1945.

In its prime, the Purple Forbidden City had many buildings and hundreds of rooms. Once vacated, it suffered from neglect, termite ravages, and inclement weather including a number of cyclones. Most destructive were man-made crises, as evidenced by the bullet holes still visible from the military conflicts of the 20th century.

Major losses occurred in 1947 when the Việt Minh seized the Citadel in February. The French led counter-attack operations where they laid siege and engaged in a six-week ensuing battle which destroyed many of the major structures. The core of the city, including the Imperial Palace, was burned.

The Citadel came under fire again in the early morning of January 31, 1968. As part of the Tet Offensive, a Division-sized force of the People's Army of Vietnam and Viet Cong soldiers launched a coordinated attack on Huế, seizing most of the city. During the initial phases of the Battle of Huế, due to Huế's religious and cultural status, United States Marines troops were ordered not to bomb or shell the city, for fear of destroying the historic structures; but as casualties mounted in house-to-house fighting, these restrictions were progressively lifted and the fighting caused substantial damage to the Imperial City. Viet Cong troops occupied some portions of the citadel while South Vietnamese troops occupied others; and allied warplanes targeted the anti-aircraft guns the communists had mounted on the citadel's outer towers. Out of 160 buildings, only 10 major sites remain after the battle, such as the Thái Hòa and Cần Thanh temples, Thế Miếu, and Hiển Lâm Các.

The city was made a UNESCO World Heritage site in 1993 as part of the Complex of Huế Monuments. The buildings that remain are being restored and preserved. The latest, and so far largest, restoration project was planned to conclude in 2015.

The grounds of the Imperial City are protected by fortified ramparts 2 by 2 kilometres (1.2 by 1.2 mi), and ringed by a moat. The water in the moat is routed from the Hương River through a series of sluice gates. This enclosure is the citadel (Kinh thành).

Inside the citadel is the Imperial City (Hoàng thành; 皇城), with a perimeter wall some 2.5 kilometres (1.6 mi) in length.

Within the Imperial City is the Purple Forbidden City (Tử cấm thành; 紫禁城), a term identical to the Forbidden City in Beijing. Access to the innermost enclosure was restricted to the imperial family.

• Đông Nam Môn (Southeast Gate), also called cửa Thượng Tứ
• Chính Đông Môn (East Gate) also called cửa Đông Ba
• Đông Bắc Môn (Northeast Gate) also called cửa Trài or cửa Mang Cá nhỏ
• Chính Bắc Môn (North Gate), also known as cửa Hậu or cửa Mang Cá lớn
• Tây Môn (West Gate)
• Thể Nhân Môn, popularly called cửa Ngăn

• Ngọ Môn (午門) (South gate)
• Hòa Bình Môn (和平門) (North gate)
• Chương Đức Môn (彰德門) (West gate)
• Hiển Nhân Môn (顯仁門) (East gate)

• Thái Hòa Điện (太和殿, Hall of Thái Hòa) ( The throne hall was built in 21/2/1805 and was rebuilt in 1833 and moved to the current location.)
• Phụng Tiên Điện (奉先殿, Hall of Phụng Tiên )
• Trường Sanh Cung (長生宮, Trường Sanh palace)
• Diên Thọ Cung (延壽宮, Diên Thọ palace)

• Triệu Miếu (肇廟)
• Thái Miếu (太廟)
• Hưng Miếu (興廟)
• Thế Miếu (世廟)
• Phụng Tiên Điện (奉先殿)
• Hiển Lâm Các (顯臨閣)

• Đại Cung môn (大宮門, Great gate to enter forbidden palace)
• Tả vu (左廡, Left hall), Hữu vu (右廡, Right hall)
• Cần Chánh Điện (勤政殿, Hall of Cần Chánh) (Working office of emperor, rebuilt in 1827, 1850, 1899 and demolished in 1947)
• Võ Hiển Điện (武顯殿, Hall of Võ Hiển)
• Văn Minh Điện (文明殿, Hall of Văn Minh)
• Trinh Minh Điện (貞明殿, Hall of Trinh Minh)
• Quang Minh Điện (光明殿, Hall of Quang Minh)
• Càn Thành Điện (乾成殿, Hall of Càn Thành) (Residential palace of Emperor until 1925, demolished in 1947)
• Khôn Thái Điện(坤泰殿, Hall of Khôn Thái) (Residential palace of Empress consort, demolished in Khai Dinh's era)
• Viện Thuận Huy Viện (順徽院)
• Dưỡng Tâm Viện (養心院)
• Ngự Tiền Văn phòng (御前文房, Office of cabinet)
• Lục Viện (六院, Six institution)
• Minh Thận Điện (明慎殿, Hall of Minh Thận )

• Ngự Uyển Viên(紹芳園, Royal garden)

• Kiến Trung Lâu (建忠樓) (Kien Trung palace, Main residential palace of Emperor and family in 1923 until the end of dynasty)
• Thái Bình Lâu (太平樓) (Reading room of emperor)

• 
  The citadel's plan in the Đại Nam nhất thống chí. The diagram is oriented with south at the top
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  The scene of medical treatment for the royal family in the Thái Y Viện
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  Enthronement of Emperor Bảo Đại in the Imperial City in 1926 with the Emperor's palanquin escorted from Hall of Diligent Governance (Điện Cần Chánh) to the Throne Hall
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  Aerial view of the Imperial City in Hue during the feast in honor of the takeover of Emperor Bảo Đại, 11 September 1932
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  Walls of the Meridian Gate
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  Meridian Gate
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  Tripod cauldrons of the Nguyễn dynasty
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  Gate
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  Flag Tower of the citadel
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  Gate of Chương Đức (彰德門)
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  Pavilion of Splendour (Hiển Lâm Các, 顯臨閣)
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  Pleasure garden in the residence of the imperial queen-mother. Hòn non bộ is installed in the lake
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  Courtyard before the Great Palace (Điện Thái Hòa) gate, with entrances to Càn Thành Hall (Điện Càn Thành) flanking both far sides of the photo
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  Flowerbed before an archway leading to Phung Tien Palace (Điện Phụng Tiên,奉先殿)

• 5182931945 Imperial City of Huế on OpenStreetMap
• view Citadel 360