Battle of Wuzhang Plains

Background
Following the withdrawal from the north during his previous campaign, Zhuge Liang focused on agricultural projects, stockpiling grain in anticipation for his next attack. He dispatched men to make repairs to the plank bridges along Xiegu Valley to facilitate the army's march. He also invented his "floating horses", rafts capable of carrying grain, which would be drawn along the Bao river.

Finally, Zhuge Liang sent envoys to Wu proposing a coordinated strike against Wei.

The Battle
In the (18 Mar.-15 Apr.) 234 A.D., Zhuge Liang led 100,000 men north, making this the largest campaign north since his first. Zhuge Liang led his troops through the newly repaired Xiegu Valley towards Mei (a city on the north bank of the Wei river, approx. 90 km west of Chang'an).

Many of Sima Yi's subordinate generals wish to stay in Mei and use the river for protection. However, Sima Yi points out that there is a great deal of harvest to the south of river and doesn't want a repeat of last time. Sima Yi moves his forces across the river and he constructs barricades on the southern shore. These fortifications also prevent Zhuge Liang simply advancing on Chang'an. The Shu forces exit the Xiegu Valley at Mei to find their advance blocked.

Emperor of Wei Cao Rui was worried about Zhuge Liang's latest incursion, so he sent General Qin Lang along with 20,000 troops to reinforce Sima Yi.

General Who Rises in Prowess Guo Huai suspected that, unable to advance east, Zhuge Liang would instead attempt to cross the Wei river and Beiyuan (north bank of the Wei opposite Wuzhang plains) and set up camp on the northern mountains. Guo Huai further said, if Zhuge Liang does encamp on the northern mountains he would isolate Longyou (the region to the northwest) then incite the non-Han tribes and people to rebel. Sima Yi thought his advice good and gave his assent.

Guo Huai moved his forces to occupy Beiyuan and he built a temporary wall there. Zhuge Liang did indeed attempt to move north and is blocked by Guo Huai.

A few days later, Zhuge Liang began to move his troops westward. Guo Huai's subordinate generals suspected he was moving to attack Xiwei (西圍, somewhere in the vicinity of Jieting). However, Guo Huai suspected it was a feint, that his actual target was Yangsui (陽遂) in the east. That he wanted to isolate Sima Yi's forces. That night, Zhuge Liang did indeed attempt to take Yangsui, but it was prepared for his attack so it did not fall.

Stalemate on Wuzhang Plains
After 2 months of manoeuvring and having been checked thrice, Zhuge Liang was forced to retreat south across the Wei river back to Wuzhang plains (possibly because he also feared his own line of communications may be cut). Having had difficulties in maintaining supplies on his previous campaigns, Zhuge Liang wanted to allay his fears by setting up agricultural colonies for a long-term engagement. Zhuge Liang used unoccupied land and worked the land to make it bountiful. He even invited the local populace to assist him, the impartiality of the Shu forces towards the Wei citizens earning great popularity among them.

At the time, the court thought the best strategy was to simply not engage the enemy; to wait for them to exhaust their supplies. And so, the standoff between the two forces at Wuzhang lasted 100 days. Many times did Zhuge Liang attempt to bait Sima Yi, but all he would do is fortify his position.

[This section should be suspect, it is from Sima Yi's Chronicles in Jin, so may be prone to embellishment]Zhuge Liang's challenges went unanswered, he attempted to enrage Sima Yi by sending women's clothing. Sima Yi was enraged and wanted to attack, so he memorialised the throne for permission. Cao Rui understood this request was merely for placating the men, that Sima Yi did not wish to fight (as a general in the field could use his own initiative to take advantage of a situation and need not ask for permission). Cao Rui sent Xin Pi with the Plenipotentiary Tally (gives Xin Pi the authority to make imperial declarations) to command all the officers to stand down.

[This section too is suspect]When an envoy of Zhuge Liang's came to ask for battle, Sima Yi inquired into Zhuge Liang's habits. Sima Yi asked about his sleeping and eating patterns, how he delivered punishment and oversaw proceedings. The envoy responded, "He wakes early and sleeps late. Punishments are always 20 or more blows, which he oversees personally. When he eats, it is only a few sheng" (a sheng is a measurement of grain; 5 sheng would be sufficient rations, but Zhuge Liang ate less than this) Sima Yi said: "Zhuge Liang takes little food and does much work; how can he last long?" Within days, Sima Yi saw a falling star and knew Zhuge Liang to be dead.

In mid Oct. 234 A.D., Zhuge Liang died from illness.

Knowing that he was ill and not long for this world, Zhuge Liang left specific instructions should the worst befall him. Zhuge Liang gave control of the army to Chief Clerk Yang Yi and said he was to retreat from Wuzhang and give command of the rearguard to Wei Yan and Jiang Wei.

Yang Yi suppressed news of Zhuge Liang's passing and quietly organised a withdrawal from the plains, but his actions came to the attention of Sima Yi, who immediately went on the attack. In response, Jiang Wei ordered the banners be raised and the drums beat, as if intending to meet Sima Yi in battle. Assuming a trap, Sima Yi immediately withdrew his forces. The ploy effective, the Shu forces retreated unmolested.

The people made this a saying, "From a dead Zhuge flees a live Zhongda." When Sima Yi heard he laughed, saying: "That is because I can take measure of the living, but not the dead!"

Sima Yi inspected the Shu camps in person and deduced Zhuge Liang was indeed dead. He reissued orders to pursue. However, by this stage the Shu forces had travelled too far, so the Wei forces broke pursuit.

The retreat successful, and the Shu forces having got through Ji Pass (Jigu), Yang Yi finally let it be known that Zhuge Liang was in fact dead. This revelation, however, brought it with it new problems.

Background
Now, Wei Yan was exceedingly brave and his martial prowess unquestionable. As such, Zhuge Liang had great faith in him and would frequently utilise him for important missions. However, Wei Yan was also proud and eager to earn renown; he considered Zhuge Liang too fainthearted and would always urge action, however dangerous (e.g. Battle of Jieting).

As for Yang Yi, he was able and quick. He performed his duties well and the troops always organised and supplies regulated; so Zhuge Liang appreciated him. However, he was also rash and narrow-minded. When all others acted humble around Wei Yan, Yang Yi alone would not make concessions.

The enmity between the two ran deep, and their intense dislike for one another was well known. Even the Sovereign of Wu, Sun Quan, had heard about their feuding. Sun Quan had said to Fei Yi, an envoy for Zhuge Liang: "Should one day there be no Zhuge Liang, they are sure to make trouble. You should take precautions." To which Fei Yi responded: "To discard them as precaution against some eventuality would be like not using boats because one would prepare against a storm. This is not a farsighted counsel."

Zhuge Liang greatly appreciated both their talents, it was only because Fei Yi mediated the situation between the two that they were able to both be used. However, now that he was dead old tensions would flare up.

The Battle
The death of Zhuge Liang having been announced, Yang Yi sent Army Advisor of the Rear Fei Yi to sound Wei Yan out.

Wei Yan had frequently disagreed with Zhuge Liang's actions, but had followed them nonetheless. With Zhuge Liang dead, and Wei Yan now occupying the most senior military position, Wei Yan thought it was finally his opportunity to engage in more aggressive operations against Wei. Wei Yan said to Fei Yi: "Although the Prime Minister had died, I am still here. The officials belonging to the Prime Minister may carry his mortal remains to be buried. I on the other hand ought to command the various troops and strike at the rebels. Because of the death of one man, must we neglect the business of the world? Besides, who am I, Wei Yan, that I should be commanded by Yang Yi to serve as general of the rear guard?"

On the surface, Fei Yi said he agreed with Wei Yan and together sign a proclamation that they would take control of the army. Fei Yi then further deceived Wei Yan by saying he would convince Yang Yi to agree to the change of control. Wei Yan let him go, but immediately regretted it. Yang Yi and his men planned to retreat, as per Zhuge Liang's orders.

Wei Yan quickly packed up his camp and headed south; he burned the plank bridges as he passed, as Yang Yi had yet to leave, and made haste towards Chengdu. Yang Yi had his men cut down trees to make a path and ordered his men to double-march in pursuit, both wanting to reach the Emperor first to make their case.

Both Wei Yan and Yang Yi memorialised the throne that the other had revolted, their express dispatches arriving on the same day. The Sovereign of Han, Liu Shan, was perplexed and asked his advisors what to make of the situation. Chief Clerk Jiang Wan and High Minister Dong Yun both sided with Yang Yi and doubted Wei Yan.

Yang Yi's forces caught up with Wei Yan at the southern end of the valley. Yang Yi dispatched Wang Ping as his vanguard to fight Wei Yan. Wang Ping shouted at Wei Yan's men, saying: "Zhuge Liang died so recently that his body in not yet cold; how dare you people act this way?" They knew they were in the wrong so abandoned Wei Yan in droves. Wei Yan took his sons and fled to Hanzhong.

Yang Yi sent General Ma Dai in pursuit of Wei Yan. Ma Dai killed Wei Yan and sent his severed head back to Yang Yi, who kicked it saying: "You slave, can you do your wicked deeds anymore?". Yang Yi had Wei Yan's family exterminated to the three degrees.

When the two missives came reporting revolt, Jiang Wan had departed Chengdu with some imperial bodyguards in an attempt to settle the situation. However, he had only travelled 5 km when he heard news that Yang Yi had killed Wei Yan so he turned back.

Aftermath
When Yang Yi returned to Chengdu, he thought he would be named Zhuge Liang's successor. However, although Zhuge Liang appreciated his talents, he did not consider the Yang Yi suitable for such a position. Zhuge Liang had instead named Jiang Wan as the next Prime Minister.

Yang Yi had always thought himself superior to Jiang Wan and so grew resentful. He commented to Fei Yi that he wished he'd defected to Wei the moment Zhuge Liang had died, which Fei Yi reported to the throne. Yang Yi was exiled to the Hanjia commandery. Yang Yi began to sow dissension in his exile so the Grand Administrator of Hanjia sent men to arrest him. Yang Yi escaped through suicide.

Fact vs Fiction
Historically...
 * ...Sima Yi has not nearly burned to death in Shangfang Gorge.
 * ...Wei Yan never had any intention of joining Wei, his revolt came about because of his deep enmity with Yang Yi.