However, Chenliu was where Cao Cao got his start, and although Cao Cao has now moved his main base to Sili, he still left a considerable amount of troops in Chenliu.
In addition, Chenliu itself is a city with high walls and deep moats, and with Cao Cao's years of management and the assistance of the Wei Family of Chenliu, it can be considered a Copper Wall and Iron Bastion. This is also why, when Chen Xi took over Yanzhou, he halted at Jiyin.
After Fa Zheng captured Yuzhou, Chenliu was actually isolated outside of Cao Cao's domain, bordered by Jiyin to the east, the Chen State of Yuzhou to the south, and Yingchuan to the southwest, effectively surrounding Chenliu on three sides.
However, at that time Liu Bei's focus was on dealing with Yuan Shao, so there was no major conflict with Cao Cao, and thus Chenliu was preserved.
