This file photo shows ancient stone fortresses in Yulin, northwest China's Shaanxi Province. (Photo by cultural heritage and archaeology team of the city of Yulin/Xinhua)

XI'AN, Nov. 13 (Xinhua) -- A comprehensive six-year archaeological survey in northwest China's Shaanxi Province has found 573 ancient stone fortress settlements, dating from the prehistoric era to the Shang Dynasty (1600-1046 BC).

This specialized investigation, carried out by the cultural heritage and archaeology team of the city of Yulin in Shaanxi from 2019 onwards, systematically searched the vast and complex terrain of the Yulin area.

Following existing water system maps to locate these ancient sites, the fieldwork involved detailed examination, specimen collection and aerial mapping of the discovered fortresses.

The survey revealed that these settlements spanned from about 2800 BC in the late Yangshao period to around 1000 BC in the Shang and Zhou (1046-221 BC) dynasties.

Mostly distributed along riverbanks, the stone fortresses were surrounded by numerous ordinary settlements without defensive stone walls, indicating a clear clustered relationship, said Ma Mingzhi, head of the team.

The development of these stone fortresses shows a clear evolution from small to large in scale, from simple to complex in layout, and from rudimentary to mature in construction techniques -- with social hierarchy becoming increasingly distinct.

The survey provides crucial information for a comprehensive understanding of the origin, development, spread and evolution of prehistoric settlements in northern China, Ma added.