Generally, Thang Long Royal Citadel in the Ly Dynasty was built under the architectural style of “Tam trung thanh quach” (three concentric circles of the citadel). The outer circle is called Dai La (La thành), the middle called Hoang thanh (Royal Citadel) and the interior named as Cam Thanh or Noi Cam and Cam Noi (Forbidden Citadel). The Cam Thanh has walls surrounding major palaces and the southern gate is Doan Mon as mentioned earlier.

The current Nung Mountain was called Kinh Thien Palace in the Le Dynasty, Thien An Palace earlier, Thien An and Can Nguyen palaces in the Ly-Tran-Le dynasties. These were the center of Thang Long Royal Citadel and Forbidden Citadel during the time of the Ly-Tran-Le dynasties. The excavation at the area planned for National Assembly House and the new Ba Dinh Hall are part of the western center of Royal Citadel and Forbidden Citadel in the Ly-Tran-Le dynasties.