Shimao

Shimao is a Neolithic site in Shenmu County, Shaanxi, China. The site is located in the northern part of the Loess Plateau, on the southern edge of the Ordos Desert. It is dated to around 2000 BC, near the end of the Longshan period, and is the largest known walled site of that period in China, at 400 ha. The fortifications of Shimao were originally believed to be a section of the Great Wall of China, but the discovery of jade pieces prompted an archaeological investigation, which revealed that the site was of Neolithic age.

The city was surrounded by inner and outer stone walls, in contrast to the rammed earth walls typical of Longshan sites in the Central Plain and Shandong. The walls were 2.5 meters thick on average, with perimeters of approximately 4200 m and 5700 m respectively, and feature gates, turrets and watch towers.

Source: Wikipedia