Deputy Director of the Yen Bai Museum Ly Kim Khoa said two of the slabs were found in Hu Tru Linh village, adding that the first, 2.8 metres high, 3.7 metres long, and 2.6 metres wide, and the other, 3.5 metres long, 1.4 metres wide, and 1.3 metres high, are fully covered with sophisticated engravings of terraced fields.

Most of the slabs, found in the second phase of a survey, had been earlier discovered by H’Mong ethnic residents while doing farm work. They are relatively close to one another, about 20 metres to 5 km apart, and located in high areas that provide a panoramic view of surrounding landscapes, including terraced fields and forests.

Local H’Mong people also bring offerings to these slabs in rituals aimed at driving away disease, evil spirits, and pestilence, Khoa added.

Staff at the Yen Bai Museum are set to continue working with experts in the time ahead to expand the survey of ancient slabs to the remaining villages in Lao Chai commune, which houses 14 villages, just five of which have by now been explored.

After finishing assessing the value and drawing a map of the slabs in Lao Chai and other communes, the provincial Department of Culture, Sports and Tourism is set to compile a dossier to seek the inclusion of the slabs into tours of the Mu Cang Chai terraced fields – a special national landscape.

In 2015, the museum carried out the first phase of the survey in Ta Ghenh and Hong Nhi Pa villages in Lao Chai commune, finding six large slabs with sophisticated engravings of terraced fields.