A rock site in the northern province of Thanh Hoa has been discovered as the excavation area used for the construction of the Ho Dynasty Citadel, which was recognized as a World Heritage Site by UNESCO in June.
Researchers from Ho Dynasty Citadel Preservation Center announced the discovery Friday after comparing the surface of stones at the rock site with those at the unique stone citadel, according to the Vietnam News Agency.
The rock site was found within An Ton mountain area of around 25,300 hectares at Vinh Loc District of the province, nearly two kilometers from the citadel where Ho Quy Ly (1336-1407) placed his central government more than 600 years ago.
A total of 21 large flagstones have been spotted around the area. These stones had not been used during the citadel construction as they were damaged, the researchers said.
Luu Tran Tieu, chairman of the National Council for Cultural Heritage, said that the finding is "especially important to the management, research and development of the Ho Dynasty Citadel."
The finding will be a "reliable scientific foundation" to support a report on the citadel, which Vietnam has promised to UNESCO after the recognition, Tieu said.
He said scientists for dozens of years have been puzzled with the question of where the stones came from to build the citadel.
While other citadels in the country until that time were built with bricks and clay, Tay Do (Western Capital) Citadel was built manually with green block granite.
Estimations from the citadel preservation center showed that around 25,000 cubic meters of stone had been used for the construction, or more than 1,000 hectares of the citadel walls.
The stones were between 10 and 20 tons each and one at the eastern wall of the citadel weighs 26.7 tons.
The construction finished in three months and the monument still stands, making it one of Vietnam's most remarkable historical sites.