Constructed in 1805, Hue Imperial City is located in the north of the Huong river. The south-facing construction covers the area of 520 hectares. There are ten main gates as follows
- Chinh Bac gate (also known as Hau gate as it is built on the back of Hue Imperial City).
- North west gate (also called An Hoa gate, the name of a nearby village)
- Chinh Tay gate
- Tay - Nam gate (Huu gate, to the right of Hue Imperial City).
- Chinh Nam gate (also called Nha Do gate as it is situated by Vo Kho where weapons are stored).
- Quang Duc gate
- The Nhon gate (also known as Ngan gate)
- South east gate (also called Thuong Tu gate as Vien Thuong Ky Institute and stable are located by the gate).
- Chinh Dong gate (also called Dong Ba gate)
- North East gate (also called Ke Trai gate).
In addition, there is another gate leading to Tran Binh Dai (a sided citadel to the north east of Hue Imperial City, also known as Mang Ca garrison or Tran Binh Mon).
The other two waterways connecting the Citadel via Ngu Ha system are Dong Thanh Thuy Quan and Tay Thanh Thuy Quan.
At first, the Imperial City was made up by earth. It was not until late Emperor Gia Long's reign that brick was used instead. Hue Imperial City is a unique combination of Vietnamese traditional architectural rules, Oriental philosophy, yin-yang and five elements theory of Chinese I Ching. The structure was affected by western military architecture named after Vauban, a French architect in late 17th century.
In Vietnamese early modern history, Hue Imperial City was considered as the largest structure. Thousands of employees and millions cubic of stones and earth were used in addition to loads of works done such as trench digging, river filling, resident relocation, etc. The construction process took place from 1803 (under Emperor Gia Long's reign) to 1832 (under Emperor Minh Mang's reign).
For defending purpose, gate and guarding pavilions were built on sides of the fortress. Bastions, cannons and ammo depots were evenly spaced. Besides, a nearly ten-kilometer-long trench system was digged along the city. Digged river system (Ho Thanh Ha) serves as not only a guarding structure, but also a waterway which is over 7 kilometers long (to the west of Ke Van river, the north of the An Hoa river, to the east of the Dong Ba river, along the Huong river to the south).
According to feng-shui geographer, Hue Imperial City is located in "Vuong dao" area which is made up by the current of the Huong river and its two branches including the Bach Yen river and Kim Long river. The Huong river takes the role as "minh duong" while the two small islets, namely Con Hen and Da Vien plays at "Ta Thanh Long" (green dragon to the left) and "Huu Bach Ho" (white tiger to the right) respectively. On the other side of the river stands Bang Son mountain which was later renamed as Ngu Binh. This range was considered as the natural guarding screen of the imperial city. The architecture of Hue Imperial City, Citadel and the Forbidden City all faced the south according to I Ching which says "Thanh nhan nam dien nhi thinh thien ha" (the Emperor faces the south to rule the country)
Based on Feng-Shui rules, Emperors of Nguyen dynasty made use of natural terrains available such as river, mountain, islets and filled a part of the Bach Yen river and Kim Long river. A number of rivers and trench inside and outside of the Imperial city was digged. These efforts showed Nguyen dynasty ‘s expectation to base here in long term. No forced arrangement, but a harmony of architecture and nature is observed at Hue Imperial City. Hue Imperial City does not impress visitors by its majesty or natural look, but brings a solemn, yet nature-harmonious feeling. Besides, its architecture and arrangement have made Hue Imperial City become the mightiest and strongest fortress in Vietnam so far. "Hue Imperial City is the most beautiful and well- proportioned fortress in Indochina, even in comparison to structures built by English such as William castle at Calcutta and Saint Georges at Madras, Le Rey, a French captain arriving at Hue in 1819 exclaimed.
Although Hue Imperial City has existed for nearly 2 centuries and was destroyed during wartime, it still stays comparatively intact. With its high values in several fields, Hue Imperial City was recognized as national historic - cultural relic on May 12th, 1998 and considered as one of the most important art architecture within Hue Monuments Complex by UNESCO. Hue Monuments Complex was recognized as a world cultural heritage on December 11th, 1993 by UNESCO.