Battle of Didao - Prelude

Prelude

In July 255, Shu general Jiang Wei decided to take advantage of the death of Wei regent Sima Shi by launching another campaign against Wei. The invasion force was one of the largest Jiang Wei had gathered in his Northern Expeditions, totalling at least 30,000 men, and including commanders such as Xiahou Ba and Zhang Yi. It is worth nothing that both Xiahou Ba and Zhang Yi held higher appointments than Jiang Wei in administrating civil affairs, but Jiang Wei was in command instead because it was a military campaign. Xiahou Ba was a blood relative of the Shu imperial family (he was an uncle of Shu emperor Liu Shan and both of his nieces were married to Liu Shan). Zhang Yi was considered more senior than Jiang Wei and Xiahou Ba as he served Shu's founding emperor Liu Bei, while Jiang and Xiahou only joined Shu after Liu Bei's death. By August 255, Jiang Wei's army took Baohan (枹罕; located northeast of present-day Linxia County, Gansu), and advanced toward Didao (狄道; present-day Lintao County, Gansu).

The newly appointed Wei Inspector of Yong Province, Wang Jing (王經), immediately notified his direct superior, General Who Subdues the West, Chen Tai, claiming that the enemy appeared to attack simultaneously on three fronts, targeting Mount Qi (祁山), Shiying (石营), and Jincheng (金城; present-day Lanzhou, Gansu), and suggesting that they should engage the enemy on those fronts. Wang Jing volunteered to lead an army to face the enemy at Shiying, and proposed having another force to defend Mount Qi. Meanwhile, Wei armies in Liang Province should be deployed to Baohan to check the enemy's advance towards Jincheng. Chen Tai was dubious about this initial intelligence since it was highly unlikely that Shu could rally such a huge army for the campaign Wang Jing perceived. Nonetheless, the Shu invasion force was one of the largest so far, and the Wei defenders could not afford to split forces. Furthermore, Wei armies in Liang Province would not be fully utilized if they were deployed elsewhere, since they would be fighting on unfamiliar terrain. Hence, Chen Tai replied to Wang Jing that they must further carefully analyze Jiang Wei's move because it was unlikely that the enemy could afford to split their forces on different fronts, and Wei must concentrate its forces to achieve absolute numerical superiority over the enemy. Wang Jing was ordered to focus on defending Didao and refrain from engaging the enemy, while waiting for the arrival of reinforcements. Chen Tai asked the Wei imperial court for reinforcements, while he led a relief army towards Chencang (陳倉; located east of present-day Baoji, Shaanxi).