A rock fortification system dating back to the 4th century in Ky Anh district, the central province of Ha Tinh has just been recognised as a National Historical Relic Site.
Ky Anh Rock Fortification was unearthed by archaeologists in 1993 on top of a local pass.
The defence system had been formed by natural dark coloured flagstones. It runs from the east to the west and measures 1km in length and 5-7m in width with average height of 4m.
There is a guard point with a firing position and accommodation for soldiers every 50m along the fortification.
Scientists from Viet Nam Archaeology Institute, the French School of Extreme Orient and the local culture sector conducted serious research at the site in 2012.
The fortification has been considered to be a part of Lam Ap Ancient Fortification, which used to run a length of more than 30km.
The Lam Ap Fortification was built by Pham Van (345-375) to protect the border.
The scientists admitted this is a uniquely designed ancient fortification with high quality architectural techniques. It has important cultural and historical value.
The Ministry of Culture, Sports and Tourism listed the site among the national art and architecture sites to facilitate preservation tasks for further research and tourism in 2014.