The citadel of the Ho Dynasty is situated in hamlets of Tay Giai, Xuan Giai (Vinh Tien Commune) and Dong Mon (Vinh Long Commune), Vinh Loc District, Thanh Hoa Province, away from Ha Noi over 150km to the south and 45km northwest of Thanh Hoa City.
The citadel of the Ho Dynasty was built in 1397 by Ho Quy Ly who was the highest-ranking mandarin of the Tran Dynasty at the time. After the citadel was completed, Ho Quy Ly forced King Tran Thuan Tong to move the capital from the citadel of Thang Long (Ha Noi) to Thanh Hoa. In the second month of the year of Dragon (1400), after coming to the crown to replace the King Tran, Ho Quy Ly renamed the country Dai Ngu (1400-1407), the citadel of the Ho Dynasty officially became the capital citadel. The citadel of the Ho Dynasty is also known as names of An Ton, Tay Do, Tay Kinh, Tay Giai, Thach Thanh.
The citadel of the Ho Dynasty is considered as the only stone citadel remaining in Southeast Asia and is one of the few remains in the world.
The citadel of the Ho Dynasty has met the two criteria specified in the World Heritage Convention. It is the criterion (ii), "to exhibit an important interchange of human values, over a span of time or within a cultural area of the world, on developments in architecture or technology, monumental arts, town-planning or landscape design," and the criterion (iv), "to be an outstanding example of a type of building, architectural or technological ensemble or landscape which illustrates (a) significant stage(s) in human history."
The citadel has recognized as a World Cultural Heritage by the UNESCO at the 35th session of the World Heritage Committee on June 27th 2011 in Paris (France).
In the world heritage record, the citadel of the Ho Dynasty is briefly described as follows:
The citadel of the Ho Dynasty, built according to the feng shui principles, testifies to the flowering of neo-Confucianism in late 14th century in Viet Nam and its spread to other parts of East Asia. According to these principles, it was sited in a landscape of great scenic beauty on an axis joining the Tuong Son and Don Son mountains in a plain between the Ma and Buoi rivers. In terms of architectural history, the citadel of the Ho Dynasty plays an important place in the planning and building of urban areas in Viet Nam. It shows the uniqueness in the construction of a citadel in general and a stone citadel in particular, and a breakthrough in Viet Nam’s tradition of building citadel. Thanks to the unique construction techniques all the major stone sections are intact and have not been affected by time and weather or by recent urban encroachment. The citadel of the Ho Dynasty is an architectural masterpiece of the 14th century with impressive architecture of the walls and other parts. The citadel buildings represent an outstanding example of a new style of Southeast Asian imperial city with a combination between the Vietnamese architecture and the unique building techniques of Viet Nam, Southeast Asia and Eastern Asia.
According to historical documents, ancient bibliographies and archaeological research, the complex of the citadel of the Ho Dynasty includes Thanh Noi (Inner Citadel and also known as Imperial Citadel) with the remains of the royal palaces and temples inside; La Thanh and Nam Giao Altar (for worshipping the Heaven).
The Thanh Noi is a unique architectural work, with its wall and four main gates made of green square stone plates beautifully carved and overlapped tightly one after another. On the average, each stone plate is 1.5m long, 1m thick and weighs about 15-20 tonnes. The citadel is fairly square with about 877m long north and south sides, 879.3m long east side and 880m long west side. Its four domed gates are called the Southern, Northern, Western and Eastern gates (or also known as the Front, Back, Left and Right gates). The stone plates on the dome are carved as sections of a grapefruit, tightly overlapping. The Front gate in the south is the main gate and has three doors. The middle door is 5.82m wide and 5.75m high. The side doors are 5.45m wide and 5.35m high. Each of three remaining gates has only one door. The wall of the citadel is 5-6m high on average. The highest wall section is the front gate with the height of 10m. Scientists estimated that the entire wall was made of 25,000m³ of stones. Inside the stone wall was another wall made of approximately 80,000m³ of soil.
According to the documents, there were palaces in the Thanh Noi such as Hoang Nguyen, Nhan Tho, Phu Cuc, Dong Cung, Dong Thai Mieu, Tay Thai Mieu, Diem Canh… However, now the Thanh Noi remains some relics such as a part of the citadel’s wall and four gates, vestiges of lakes, a couple of stone dragons with sophisticated carving features, foundation of Thanh Noi architecture, Hoa Nhai marble-paved road, stone balls, stone bullets, pottery, the Southern gate precinct and valuable objects with specific characteristics of Tran - Ho dynasties culture.
Called Hao Thanh, the system of water trench surrounded the Thanh Noi and connected with Buoi River through a canal at the southeast corner of the citadel. The Hao Thanh had four stone bridges over to the Thanh Noi at the four gates. Nowadays, many parts of the Hao Thanh have been filled and dried. However, the traces of the Hao Thanh still can be seen very clearly in the north, east and south of the citadel.
The La Thanh, the outer wall of the citadel built to protect the Thanh Noi was home to residents in the citadel. The La Thanh was approximately 10km in perimeter and its construction based on the natural terrain. The Ho Dynasty built the La Thanh by banking up and making bamboo hedge to connect the mountains of Don Son (Vinh Thanh Commune), Hac Khuyen (Vinh Long Commune), Xuan Dai, Trac Phong, Tien Sy (Vinh Ninh Commune), Kim Ngo (Vinh Tien Commune), Kim Nguu, Tuong Son (Vinh Quang Commune) with two rivers of Buoi and Ma. Now, the trace of La Thanh in Beo Village (Vinh Long Commune) with a length of 2000m has been localized for protection.
The Nam Giao Altar, an importance royal architectural work, was built in 1402 in the southwest of Don Son Mountain, on the spiritual pathway directly connected with the Southern gate, about 2.5 km away from the citadel of the Ho Dynasty to the southeast. The Nam Giao Altar has an area of 43,000m². Currently, the altar appears 5 grounds with 5 terraces. There is a difference of 7.80 meters between the highest and the lowest. The Nam Giao Altar is the place to sacrifice to the heaven; pray for harmonious rain and wind, peaceful country and happy people, prosperous and everlasting dynasty. In addition, the altar is also the place to sacrifice to the soul of dead kings, stars and many other genies. Nam Giao ceremony is considered as a royal ritual. The first Nam Giao ceremony of the Ho Dynasty was held in the same year of constructing the altar.
At the citadel of the Ho Dynasty, apart from construction of the Nam Giao Altar and performance of Nam Giao ceremony in 1402, the Ho Dynasty had left historical marks such as establishing Xa Tac Altar (altar of the Earth Genie and the Shennong - the Divine Farmer) in 1397, organizing two state exams in 1400 and 1405. In addition, the Ho Dynasty had been associated with remarkable innovations, such as reforming examination, building more schools, heightening the Nom scripts and issuing paper-money.