Taosi () is an archaeological site in Xiangfen County, Shanxi, China. Taosi is considered to be part of the late phase of the Longshan culture in southern Shanxi, also known as the Taosi phase (2300 BC to 1900 BC). Archaeology Taosi was surrounded by a gigantic rammed-clay enclosure. This was discovered from 1999 to 2001 by the archaeologists from the Institute of Archaeology, Chinese Academy of Social Sciences; they attributed this wall to the Middle Taosi period (4,100 to 4,000 BP). Rectangular in form with an inner area of 280 ha. An internal rammed-earth wall separated the residential and ceremonial areas of the elite from the areas inhabited by commoners, signifying the development of a stratified society. A painted stick discovered from a prehistoric dating from 2300 BCE excavated at the astronomical site of Taosi is the oldest gnomon known in China. The gnomon was widely used in ancient China from the second century BC onward in order determine the changes in seasons, orientation, and geographical latitude. The ancient Chinese used shadow measurements for creating calendars that are mentioned in several ancient texts. According to the collection of Zhou Chinese poetic anthologies Classic of Poetry, one of the distant ancestors of King Wen of the Zhou dynasty used to measure gnomon shadow lengths to determine the orientation around the 14th-century BC. The Huaxia settlement outgrew the perimeter of the wall. The settlement is the largest Longshan site discovered in the Linfen basin, Yellow River basin area, possibly a regional center. The settlement represents the most political system on the Central Plains at the time. The polites in the Taosi site are considered an advanced chiefdom, but may not have not developed into a higher political organization. It was not the Taosi pelites but, the less socially complex Central Plains Longshan sites, the scattered, multi-system competing systems that gave rise to early states in this region. Ancient "observatory" Taosi also contained an astronomical observatory, the oldest in East Asia. This was discovered in 2003-2004. Archaeologists unearthed a Middle Taosi period semi-round foundation just beside southern wall of the Middle Taosi enclosure, which could be used for astronomical observations. The structure consists of an outer semi-ring-shaped path, and a semi-round rammed-earth platform with a diameter of about 60 m. The platform is 42m in diameter and over 1000 sq m in area, and can be reconstructed as a three-level altar. On the