During the period of Nguyen Lords, Hue was chosen as the capital of Southern Viet Nam (Dang Trong). The Lords Nguyen Phuc Lan and Nguyen Phuc Tan established a chief town in Kim Long between 1635 and 1687; Lords Nguyen Phuc Thai and Nguyen Phuc Khoat moved it to Phu Xuan in 1687-1712 and 1739-1774. Hue had been the capital of Quang Trung Nguyen Hue king-Tay Son period, and then became the capital of the united Vietnam when Nguyen Phuc Anh ascended the throne starting Nguyen dynasty which lasted 143 years. With its history closely connected with nine Nguyen Lords who were ancestors of later Nguyen emperors, it is understandable that Emperor Gia Long selected land lying in the middle of the country to build the Citadel for the Nguyen dynasty.
Originally the Citadel walls were made of soil. It was not until late in Emperor Gia Long’s reign that the walls were constructed of brick. Hue Citadel is an original combination embracing traditional Vietnamese architectural principles, Oriental philosophy, the Chinese principles of Yin and Yang and of the five basic elements of the earth, together with an influence drawn from Vauban-styled architecture of military in the Occident. (Vauban was a French architect at the end of the 17th century).
Hue Citadel is the most grand of the structures built in recent Vietnamese history. Its creation required ten of thousands of builders; millions of cubic meters of soil and rock; dangerous activities such as building wall embankments and digging the moat while the river was in full flow; removing and re-locating graves; and so forth lasting from 1803 under Gia Long’s reign until 1832 during Emperor Minh Mang’s period.
Built for defence purposes, the Citadel consists of a square of fortified walls with the wall situated along Huong River having a slight outward curve to follow the bend in the River. The external walls total almost 10 kilometres in length and are about 2 metres thick. Spread evenly around the walls are 24 bastions which enabled the use of an arsenal of rockets and cannons.
In addition, the moat system surrounding the wall is about ten kilometers in length. Outside the moat is seven kilometres of canal which flows in to the Huong River at two points. The moats and canals served both as a defence system and as waterway transportation. The west waterway is Ke Van canal, to the north is An Hoa canal, to the east is Dong Ba canal and on the south is the Huong River.
In the external walls there is a total of ten entrance gates, each topped by a covered observation post or watch tower, and reached by crossing a bridge over the external moat. There is an additional gate on Phu Binh at the north-east of the Citadel.
- Chinh Bac Entrance, also called Cua Hau entrance, is on the NNW wall furthest from the Huong River.
- Tay Bac entrance, also named Cua An Hoa entrance after the name of a local village, is also on the NW wall.
- Chanh Tay entrance is on the SW wall.
- Tay Nam entrance, also called Cua Huu entrance, is on the SW wall.
- Chinh Nam, also called Cua Nha Do entrance since it is situated close to the arsenal built up by Emperor Gia Long, is in the SE corner facing the Huong River.
- Quang Duc entrance is slightly SW of Cot Co, the huge Flag Tower at the front of the Citadel.
- The Nhon Gate is also known as the Ngan Gate because it was surrounded by a high wall creating a path reserved for the king to walk to the river (ngan) bank.
- Dong Nam entrance is also called Thuong Tu Gate as the royal stables were behind this entrance and it was used as a Citadel entry point for horses.
- Chinh Dong entrance, also named Cua Dong Ba entrance after a local village, is on the east wall.
- Dong Bac entrance, also called Cua Ke Trai entrance, is in the NE corner of the Citadel.
- Tran Binh Mon, also known as Cua Tran Binh, provides an external entrance link to Phu Binh island, at the northeast corner of the Citadel.
Two water gates, Dong Thanh Thuy Quan and Tay Thanh Thuy Quan, cross the water flowing out of the Citadel from the Royal Canal.
The Citadel site was chosen on the advice of geomancers. Based on geomancer principles, Nguyen kings linked available features of the natural terrain such as rivers, mountains, islands, together with man-made additions and alterations. The added features included filling in several parts of such rivers as Bach Yen, Kim Long and and digging a series of canals and moats within and around the Citadel to implement their grand plan.
Hue Citadel lies on an “imperial island” created by the Huong River’s flow at the front and from two tributaries namely Bach Yen and Kim Long flowing behind the present walls and joining together. Huong River plays the role of “ming-tang” and the two small islands, named Con Hen and Con Da Vien, are in the positions of Left Blue Dragon and Right White Tiger guarding the Imperial city. Near the river there is Bang Mountain, which was renamed as Ngu Binh, sitting in front of the capital and providing a natural screen. The Citadel and all the architectural structures of the Citadel, including those of the Forbidden Purple City, face the south, following the prophet’s direction in the Book of Changes (I Ching) “the ruler faces the south to rule the nation”
The Hue Citadel was the most magnificent protective construction built in modern times. It took thousands of workers and the huge undertaking commenced in 1803, during Gia Long's reign, and was completed in 1832 by his successor Minh Mang. The design of the facade followed the natural terrain of the Huong River’s north bank. Each wall of the Citadel contained entry gates with watch towers, bastions with canons and ammunition depots. The Citadel was defended by a moat system surrounding the wall and the man-made canals and rivers not only provided water defences but also water transportation.
The aspirations of the Nguyen Emperors were accomplished by human effort and skill. It is difficult to appreciate that the harmony evident in the Citadel site was not provided by nature alone but results from a restrained and complex combination of natural environment, inspired design and human endeavours.
The Citadel is neither oppressive, nor wild. Within its walls people can experience solemnity without losing the tranquility of nature. The combination of natural scenic beauty with architectural style and defence requirements assisted Hue Citadel in becoming one of the most imposing and majestic constructions in Indochina.