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.

The main part of Imperial Citadel of Thang Long – Hanoi essentially covers a large area of 20 ha consisting archaeological area at 18 Hoang Dieu Street and relics in Hanoi 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.