Beijing, April 18 (IANS/EFE) Archaeologists have discovered three previously unknown sections of the Great Wall in the northwestern region of Ningxia.

The segments, which together span some 20 metres, were found near Nanchangtan, the former curator of the Museum of the Ningxia Hui Autonomous Region told Xinhua.

The newly-found sections are thought to be more than 2,400 years old and formed part of the Great Wall built by the Qin Dynasty (221-206 BC), Zhou Xinghua said.

Emerging triumphant from the Warring States Period (475-221 BC), the Qin state erected massive barriers in the Yellow River valley to prevent would-be invaders from marching across the river when it was frozen, Zhou said.

The UN Educational, Scientific and Cultural Organisation designated China’s Great Wall as a World Heritage Site in 1987.