In 1998 an exploration excavation at Doan Mon, Cua Bac and Hau Lau found many relics and artifacts from the Ly and Tran Dynasties. In 2008 another excavation at the site between Doan Mon and the foundation of Kinh Thien Palace found vestiges of the court in front of the royal palace from the Le Dynasty, which was built with wooden bricks, a typical type of that time. Particularly, from December 2002 to 2004 an archaeological excavation was carried out at No. 18 Hoang Dieu Street and found a complex of relics and artifacts on an area of 19,000m² which date back to the pre-Thang Long time before the 11^th century through Thang Long to Hanoi time. Later, the excavation area was expanded to 33,000 m² where overlapping cultural layers with relics of architecture, sewerage systems, water wells, foundations, pillars and walls and vestiges of old rivers and lakes were discovered. All these show the continuous history and culture with diverse layers of a palace area which had existed through different historical periods. The centre sector of the Imperial Citadel of Thang Long – Hanoi has three outstanding characteristics:

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Firstly, although the heritage area is not large, it was a centre of power and culture for 13 consecutive centuries (from the 7^th century up to now), including over eight centuries (from the Ly Dynasty in the 11^th century to the Le Dynasty in the late 18^th century) as a political and administrative centre of a nation, which developed early in Southeast Asia, until today. This is a unique characteristic rarely seen in the history of other imperial cities in the world.

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Secondly, as a centre of power and a centre of the imperial citadel, the heritage area contains a fusion of historical and cultural values of the nation. The forbidden city served as the working place of the court where political, cultural, religious and diplomatic ceremonies of the royal dynasty were held, and was the residence of the royal family. So it was home to palaces, castles with architectural art and technique, construction plans and landscape building which were carried out by talented people. The excavation has found relics of many large-scale palaces of different types, beautiful decorative items and utensils of high technical and artistic value of the royal family. It may be said that the heritage site reveals the cultural quintessence of a nation.

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Thirdly, when setting up the capital city in Thang Long, King Ly Thai To considered this place as “a position between the earth and the heaven”, “a position between the North and South, East and West”, which “overlooks the river and leans against the mountains”, “an essential meeting place of the four directions”, etc. In terms of natural conditions, Thang Long was the centre of the Red River delta, a cradle of the wet rice civilization of the Viet people and the hub of domestic and international water-way transport system via the Red River axis. It was due to this favourable position and the construction efforts of the royal dynasties, Thang Long has become an eternal capital city until now. It was this position that helped the heritage site have broad contacts and interactions with the world, which is shown in the fact that many artifacts coming from West Asia, China, Japan, Korea, etc., were found in the archaeological relic site.

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From these outstanding characteristics, the central sector of the Imperial Citadel of Thang Long – Hanoi bears not only the quintessence of national cultural values but also of globally significant values, meeting the criteria (2, 3 and 4) of the world cultural heritage.

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For these reasons the heritage site was classified as a relic of national-level on December, 28, 2007 and of special national-level on August 12, 2009. In particular, on July 31, 2010 (August 1, 2010 of Vietnamese time), at the 34^th session of UNESCO’s World Heritage Committee held in Brazil, the Central Sector of the Imperial Citadel of Thang Long – Hanoi was list as the World Cultural Heritage.