The sphere of the area of the capital city Pingcheng needs research in a roundabout way because of lack of historical records. The Northern WEI Dynasty set up its capital in Pingcheng and appointed the county magistrate . In the capital city as well as on its suburbs, DAI Prefecture was established with the DAI magistrate as the governor because of following the pattern of confering upon Yilu for DAI State in the Western JIN Dynasty, or the DAI Prefecture in the pre-QIN Dynasty. Sizhou was set up in DAI Prefecture including the area around. Sizhou was also called the suburban of the capital with Xiaowei or the prefecture governor as the ruler. Examining the historical records, the geographical area of the suburban of the capital city before the Northern WEI Dynasty should be: the boundary to the north was Yen Mountain, Taihang Mountain to the east, Hengshan Mountain to the south and along the Yellow River reaching the Hetao to the west. After the era of TAIWU, the sphere of the area of the capital city reduced in all directions. The area was bounded by the six towns to the north, Taihang to the east, Hengshan to the south and the Yellow River and Shuozhou to the west. On the tenth year of TAIHE of emperor Xiao Wen when Sizhou was rebuilt, it was reduced to an area limitted to Datong city, Shuozhou city and the southern area of lining city in inner Mongolia.