In 196 Cao Cao brought Emperor Xian to Xu county. Until Cao Pi replaced the Han, a great many edicts were issued from here. The later phrase “hold the emperor and command the lords” means Xu. Wei renamed the county Xuchang in 221, so the modern name is a step later than the Jian’an name.
The field of Guandu is northeast of Xu, near modern Zhongmou, not inside the later city of Xuchang. Cao Cao could face Yuan Shao with a smaller army partly because Xu gave him the emperor and a base for agricultural colonies. Guan Yu’s short service under Cao Cao, the killing of Yan Liang, and the departure also belong to this political center.
Xuchang later yielded the first place among capitals to Luoyang and Ye. It remains the starting point for how Cao Cao turned the north into a state.