The Zhou Dynasty has been habitually called the Eastern Zhou since King Ping moved the capital to Luoyi in 770BC. It fell into two periods: the Spring and Autumn period and the Warring States period. After the moving of the capital, the emperor's power was weakened and reduced helplessly from "the common lord under the sun" to a vassal for protection from the strong kingdoms around. The Spring and Autumn period saw the annexation of several scores of states into seven powers, and this period is known as the Warring States period (475BC-221BC) for the nibbling and swallowing among the states over a long period of time. The Beijing district is the proper place where the State of Yan, one of the seven powerful states, located, with Ji as its capital.

During the Warring period, the seven powers contended to strengthen the fortification to handle with the frequent wars. At that time, the fortification walls were built in the states of Yan, Qin, Chu ,Zhao and Wei, etc. The state of Yan also had the fortification walls built to defend against the state of Qi and Zhao in the south and the Rong Di minorities in the north. There were two such walls in the state of Yan: the north one and the south one. The north one started at Zaoyang(the present Huailai County in Hebei Province) in the west and ended at Xiangping(the north corner of the present Liaoyang County in the province of Liaoning) in the east. The dike in the county of Yishui was expanded into the south one which winded from the southwest of the present Yi county in the west to the present Wen'an County in the east. In the meanwhile, quite a few castles or towns were set up in thepincedom for defense and outward expansion. Only in the Beijing district a number of ancient castles or towns now have been found exactly at the places of Doudian, Changgou, Caijiazhuang. They were all in the southwest to Beijing proper and were located on one line from Lower Capital of Yan (the present Yi County in Hebei Province) to Ji (the southwest of the Beijing city). The line goes northeastward and the distance between the towns or castles were approximately equal. Besides Ji, there were Central Capital and Lower Capital. The name of Central Capital of Yan was recorded in such historical literature as Liangxiang County of You Region , Volume 69 of Geographical Records Composed in the Taiping Reign, which reads "(The place) was Central Capital of the State of Yan, and Liangxiang County of Zhuo Commandery in the Han Dynasty."