A quarry that provided the material to build the Ho Dynasty Citadel has been discovered 2km northwest from the citadel in the central province of Thanh Hoa.

Ho Dynasty Citadel's Heritage Preservation Centre Director Do Quang Trong said that a group of archaeologists discovered the quarry while studying the area around the citadel.

It is located in Vinh Loc district's Vinh Yen commune, cut out of a cliff that rises 126.5m and covers an area of over 25ha.

The centre has unearthed 21 flagstones scattered across a wide area.

Based on cutting marks on the surface of the stones and comparisons with stones from the citadel, experts said that the stones were intended for the citadel but discarded because of faults such as cracks and size.

Luu Tran Tieu, Chairman of the National Council for Cultural Heritage said it was an important discovery in the context of the citadel's history. "The province should work quickly to protect the area. Moreover, they need to continue their work to add scientific basis to their theory and report it to the United Nations Educational, Scientific and Cultural Organisation (UNESCO)," he said.

For many years, local and international researchers have wondered where the stone for the citadel came from. There have been a number of theories but until now, nothing solid.

This discovery plays an important role in opening a new way of researching stone exploitation and transportation techniques.

The citadel was built under the reign of King Ho Quy Ly and became the capital of Vietnam from 1397 to 1407.

According to estimations, about 25,000 cu.m of stone was used to build the walls of the citadel, and each stone had an average weight of 10-20 tonnes.

On account of its unique architectural and historical values, it was recognised as a World Culture Heritage by UNESCO in June 27, 2011. /.