Zhang Song
Their opportunity came in 211, when Liu Zhang became fearful upon receiving news that Cao Cao was planning to attack the warlord Zhang Lu in Hanzhong Commandery. As Hanzhong Commandery was located strategically at the northern route leading into Yi Province, Liu Zhang would be in great peril if Hanzhong fell into Cao Cao's hands. Zhang Song proposed to Liu Zhang to invite Liu Bei to Yi Province to assist them in countering the threat posed by Cao Cao. Liu Zhang agreed and sent Fa Zheng as his envoy to contact Liu Bei. When Fa Zheng met Liu Bei, he secretly told him, "General, with your brilliance, you can overcome our incompetent and weak Governor Liu. Zhang Song, as a trusted adviser (of Liu Zhang), will serve as your spy. Upon acquiring Yi Province's wealth and resources, and having its natural barriers as protection, you can easily realise your grand ambitions." Liu Bei accepted Fa Zheng's advice and led his forces into Yi Province, where he met Liu Zhang at Fu County (涪縣; present-day Fucheng District, Mianyang, Sichuan). Liu Bei then led his troops north to Jiameng (葭萌; located about 20 km northeast of present-day Jiange County, Sichuan) before turning south to attack Liu Zhang later.