In April 211, Cao Cao sent
Zhong Yao and
Xiahou Yuan to lead an army to attack
Zhang Lu in
Hanzhong Commandery. As they were due to pass through the
Guanzhong region along the way, Gao Rou advised Cao that by sending a large army westwards,
Ma Chao and
Han Sui would believe that the army was targeted at them; they would then rise in rebellion. What Cao Cao should do was to first pacify the Guanzhong region; once the region is stabilised, Zhang Lu would surrender once an edict was issued to him. Cao Cao ignored Gao; when Zhong Yao entered Guanzhong, Ma and Han did indeed rebel. ==Service under Cao Wei==