contacts between the regions. There were also expansions from middle and late Dawenkou sites (3500-2600 BC) toward central Henan and northern Anhui which coincides the era of maximum marine transgression. Late period The late period (2600 to 2000 BC) of the Longshan culture in the middle Yellow River area is contemporaneous with the classic Shandong Longshan culture. Several regional variants of the late middle Yellow River Longshan have been identified, including Wangwan III in western Henan, Hougang II in northern Henan and southern Hebei, Taosi in the Fen River basin in southern Shanxi, and several clusters on the middle reaches of the Jing River and Wei River collectively known as Kexingzhuang II or the Shaanxi Longshan. As the Neolithic population in China reached its peak, hierarchies of settlements developed. In physically circumscribed locations, such as the basin of the Fen River in southern Shanxi, the Yellow River in western Henan (confined by the Zhongtiao Mountains and Xiao Mountains) and the coastal Rizhao plain of southeast Shandong, a few very large (over 200 ha) centers developed. In more open areas, such as the rest of Shandong, the Central Plain (in Henan) and the Wei River basin in Shaanxi, local centers were more numerous, smaller (generally 20 to 60 ha) and fairly evenly spaced. Walls of rammed earth have been found in 20 towns in Shandong, 9 in the Central Plain and one (Taosi) in southern Shanxi, suggesting conflict between polities in these areas. Shandong Longshan The center of Shandong is a mountainous area, including Mount Tai (1,545 m) and other several other peaks over 1000 m. Longshan settlements are found on the plains surrounding this massif. To the north are four evenly spaced walled centers, Chengziya, Dinggong, Tianwang and Bianxianwang (from west to east), with the largest, Chengziya, enclosing only 20 ha. A pottery sherd inscribed with 11 symbols was found at Dinggong, but scholars disagree on whether it should be dated to the Neolithic period. The largest sites yet found in Shandong are Liangchengzhen (273 ha) and Yaowangcheng (368 ha). Both sites are near the southeast coast in the Rizhao area, with Yaowangcheng about 35 km to the south of Liangchengzhen. Each site is surrounded by a hierarchy of economically integrated settlements, but there are relatively few settlements in the area between the two, suggesting that they were political centers of rival polities. Production of pottery, stone tools and textiles