Under the reign of Minh Mang emperor, when all architectures of the Imperial City were replanned, Nam Khuyet Dai was replaced by the large-scaled Ngo Mon with 5 entrances arranged in U-shape. The middle entrance was for the king, the left and right-sided entrances were for civil and military mandarins. The rest two entrances were for soldiers, elephants and horses. On the top of Ngo Mon was Ngu Phung Pavilion with 100 iron-wood columns and the refined roof system symbolizing for the peace and prosperity.

Ngo Mon is not only the main entrance of Imperial City but also the place for royal ceremonies, such as the New Calendar Delivery ceremony, the parade of royal troops, the Successful Candidate Proclamation of the National Examination, the receiving ceremony of ambassadors, etc. It is also the historic construction witnessing the historical event when the monarchical regime transferred its power to the democratic regime in August, 1945. For these reasons, Ngo Mon has cultural and historical significance of not only Hue people, of the country and nation, but also of the human being in the role of the World Cultural Heritage.

Under the impacts of climate and wars, Ngo Mon was repaired many times. In the latest restoration between 1992-1993, it was restored by 100,000 USD - valued financial support of the Japan Fund-in-trust via UNESCO. After 20 years, Ngo Mon is now in need of urgent preservation. Hue Monuments Conservation Center has conducted the survey to set up project of Ngo Mon preservation in cooperation with the Institute of Monument Conservation. The project compilation has been finished and expected to receive 100 billion VND from the State Bank of Vietnam’s grant for the implementation. Presently, HMCC is carrying out the necessary procedures to start the preservation in 2013.