The central sector of Imperial Citadel of Thang Long – Ha Noi covers area of 20ha, includes archaeological area at 18 Hoang Dieu Street and relics in Ha Noi Citadel such as: Bac Mon, Doan Mon, Hau Lau, stone dragons in Kinh Thien Palace, dragon house, house D67 and Ha Noi flag tower. These relics are surrounded by 4 streets: Phan Dinh Phung Street in the north, Dien Bien Phu Street in the south, Nguyen Tri Phuong Street in the east and Hoang Dieu Street in the west.
In 1009, Ly Cong Uan was enthroned, founded Ly Dynasty. In July, 1010, the king promulgated Chieu Doi Do (the royal decree) to change the capital city from Hoa Lu (Ninh Binh) to Dai La Citadel. After transferring the capital city, Ly Cong Uan had Citadel of Thang Long built and the citadel construction was finished in early 1011. The ancient Citadel of Thang Long was encircled by three incorporated forts. The outer fort was Kinh Thanh (Imperial City), where the general public lived. Surrounded by the Hong, To Lich and Kim Nguu rivers, Kinh Thanh acted as a dyke system for the capital city. The second fort (the middle ring) was Hoang Thanh (Imperial Citadel), where the royal court, offices and residence of mandarins were located. The smallest and most inner enclosure was Tu Cam Thanh (Forbidden City) where the king, queens and concubines lived in seclusion. The Citadel of Thang Long was repaired and had many new works in Tran Dynasty and expanded in Le So Dynasty. From 1516 to 1788 in dynasties of Mac and Le Trung Hung, the Citadel of Thang Long was destroyed many times. In early 1789, King Quang Trung transferred the capital city to Phu Xuan, the Citadel of Thang Long only acted as Bac Thanh (the northern defensive fortification). In Nguyen Dynasty, the remainders of the Imperial Citadel of Thang Long were transferred to Phu Xuan for building new citadel. Only Kinh Thien Palace and Hau Lau were retained to be accommodations for Kings Nguyen during their business trips to the Bac Thanh. In 1805, King Gia Long ordered the demolition of walls surrounding the Imperial Citadel of Thang Long and requested the building of a new, smaller citadel called Ha Noi Citadel with architectural style of Vauban (France). In 1831, King Minh Mang changed name of the Citadel of Thang Long to Ha Noi Province in a big administrative reform. When French colonists occupied all Indochina, they chose Ha Noi as the capital of French Indochina Union and the Ha Noi Citadel was destroyed to build military camp for French colonists. Since the Vietnamese army took the control of the capital city in 1954, the Ha Noi Citadel has become the headquarters of the Ministry of Defense. The first value of the central sector of Imperial Citadel of Thang Long – Ha Noi shows that it is nearly a book displaying over 10 century- history of Thang Long – Ha Noi from Dai La Citadel in Pre-Thang Long period to nowadays.
History revealed that Imperial Citadel of Thang Long changed a lot but its centre, especially Forbidden City, remained nearly unchanged. As architectural structures inside the Imperial Citadel were rebuilt and upgraded several times, this explained for the findings of layers of architectural vestiges and artefacts at archaeological site at 18 Hoang Dieu. These vestiges reflect clearly relation between urban project and architectural space as well as succession of dynasties in building the Citadel of Thang Long. This is the unique and prominent value of the central sector of Imperial Citadel of Thang Long – Ha Noi. Here, archaeologists excavated a great deal of porcelain and ceramic wares used in the Imperial Citadel through various stages of development. The findings paved the way for researchers to study ceramics made in Thang Long and ceramic wares used in the Imperial Citadel of Thang Long through different dynasties. It is also concrete evidence about high development level of economy and culture. In addition, porcelains and bronze coins of China, Japan, Western Asia… found here proved that Thang Long was centre of cultural exchange among countries in area and received quintessence values of humanity. At 20h30 on July 30, 2010 in Brasilia Capital of Brazil, World Heritage Committee of UNESCO recognized the central sector of Imperial Citadel of Thang Long – Ha Noi as world cultural heritage based on three prominent criterions: historical and cultural length; its continuousness as a power centre; diversification and plenty of vestiges and artifacts. In opening ceremony of the 1000th anniversary of Thang Long – Ha Noi on October 1, 2010, Ms Irina Bokova – General Director of UNESCO gave certification of the central sector of Imperial Citadel of Thang Long – Ha Noi to leaders of Ha Noi City.