在三国时期，蜀汉的丞相诸葛亮计划北伐曹魏，名将魏延提出了一个叫做子午谷奇谋的战略计划。这个计划是这样的：魏延亲自带领一支万余精兵从子午谷迅速赶到达长安，一举拿下了长安和潼关，而诸葛亮的大军则从斜谷进攻长安和潼关，两军在潼关会师。然而，这个计策过于危险且难以成功，所以诸葛亮 ultimately rejected it. Some people believe that by not using this plan, he missed a great opportunity; others think that his true intention was to first capture the strategic city of Liangzhou (凉州) and then gradually expand into Cao Wei's territory.

The Subei Valley, also known as Suidong Valley or Zimudu Valley, is a valley in southern Shaanxi Province, stretching approximately 330 kilometers from north to south. It starts at the western foothills of the Qin Mountains near Chang'an County and ends at Shiquan County. The valley is surrounded by steep cliffs and numerous staircases due to its location within the Qin Mountains range. As recorded in "Zizhi Tongjian," Subei was once part of Baozhong County under Hanzhong Prefecture during Wang Mang's rule.

During his initial northern expedition against Cao Wei, General Wei Yan proposed an audacious plan called the "Subei Valley Surprise." He led five thousand elite soldiers through the treacherous Subei Valley to swiftly reach Long'an City below and capture it with ease. Meanwhile, Zhuge Liang led their main force from Xialu Pass towards Long'an for reinforcement. However, Zhuge Liang deemed this plan too perilous and unlikely to succeed so he decided not to implement it.

Wei Yan believed that Zhuge Liang had been overly cautious in rejecting his proposal while some historians argue that Zhuge Liang never intended to attack Long'an but rather aimed for capturing Liangzhou first before methodically encroaching on Cao Wei's territories.