Guan Yu's army was unstoppable, capturing many towns in the Central Plains, and Cao Cao was extremely anxious, as none of his generals could defeat Guan Yu; if things continued this way, Guan Yu would eventually march against him. After much deliberation, Cao Cao decided to ask Sun Quan for help. He wrote a letter, stating that if Sun Quan would send troops to intercept Guan Yu, he would cede the Jiangnan region to him. Sun Quan considered the offer and agreed.
There had long been tensions between Sun Quan and Liu Bei, and over the issue of Jingzhou, the two nearly came to blows; had it not been for the threat posed by Cao Cao at the time, which forced them to join forces against him, war would have broken out between them much earlier. Many generals in Eastern Wu had always advocated for reclaiming Jingzhou, with Gan Ning and Lu Su being among the leading voices, arguing that Jingzhou's advantageous geographical position was beneficial for military campaigns and consolidating their base. If Liu Bei's power had not grown so rapidly, Sun Quan might not have allied with Cao Cao.
Because the rise of Liu Bei's forces would inevitably threaten the existence of Eastern Wu, and with Cao Cao and Liu Bei growing increasingly powerful while Eastern Wu grew weaker, how could Sun Quan feel at ease? For these reasons, Sun Quan agreed to form an alliance with Cao Cao. By this time, Guan Yu had already advanced to Xiangyang City, encountering almost no resistance. Sun Quan gathered his subordinates to discuss countermeasures, and Lü Meng volunteered to lead the campaign, offering his own suggestions. Lü Meng held a high position in Eastern Wu. In the past, he disliked reading and rejected scholars, but later, persuaded by Sun Quan, he immersed himself in military texts and historical records, mastering many battle strategies, and eventually became a military strategist.
Lü Meng proposed that General Sun Jiao, the Conqueror of Barbarians, station troops at Nan Commandery, that Pan Zhang garrison Baidi City, and that Jiang Qin lead ten thousand men to patrol along the Yangtze River, engaging any enemy they encountered, while Lü Meng himself would take the main force to Xiangyang. Lü Meng understood that Guan Yu was arrogant and looked down on others, inevitably despising the Wu army, and precisely for this reason, he had to seize the opportunity to eliminate Guan Yu; otherwise, once Liu Bei's power grew, Wu would be left gasping for breath, vulnerable to being trampled upon.
Sun Quan did not immediately express his stance, but Lü Meng argued that they should seize the opportunity to take back Jingzhou. Sun Quan, of course, desired the same. After carefully considering Lü Meng's words, he finally decided to attack Jingzhou. Sun Quan and Lü Meng led their troops to a crossroads and sent a soldier to scout the situation at Fancheng. The scout reported that Shu forces had set up numerous defenses there. This was something Lü Meng had not anticipated—Guan Yu's defenses were so formidable that Lü Meng had to devise an alternative plan. Lü Meng suggested to Sun Quan that they appoint an obscure general to replace him as commander of the main army, while spreading word that he was seriously ill. Lu Xun was the most suitable candidate, as almost no one had heard of him or knew of any achievements he had made. Guan Yu always looked down on his opponents, and facing Lu Xun, he would surely become even more contemptuous. They could also have Lu Xun deliberately show weakness, making Guan Yu let his guard down against the Eastern Wu forces. This way, they could strike when the enemy was unprepared.
Indeed, after Lu Xun took office, he sent a letter to Guan Yu. Upon receiving it, Guan Yu was overjoyed and repeatedly praised Lu Xun as a clever man. However, Guan Yu did not realize that he had already been set up—a few flattering words of praise made him lose all caution. In the letter, Lu Xun expressed a desire for peaceful coexistence with Guan Yu and hoped to resolve the conflict through friendly means, even asking Guan Yu for guidance and favor. After reading it, Guan Yu felt smug and contemptuously dismissed Sun Quan's generals as worthless, thinking to himself about transferring more troops from the garrison at Fancheng to the front lines. When Lü Meng secretly saw that Guan Yu had moved some of the Fancheng defenders, he hastily led a group of elite soldiers to Xunyang.
Lü Meng sent people to gather many boats, hiding most of his soldiers inside the cabins, and then piled up boxes used by merchants for transporting goods outside the cabins. He also ordered the remaining soldiers to discard their armor and wear only ordinary clothes. Lü Meng disguised himself as a merchant and stood on the boat, commanding the soldiers to row along the Yangtze River toward Jiangling. Guan Yu had set up many checkpoints along the Yangtze River. When Lü Meng's fleet passed these checkpoints, the Shu army always believed they were just merchant ships and did not suspect anything at all, resulting in all of them being subdued by Lü Meng's men. At this time, Guan Yu was still fighting on the front lines, completely unaware of Lü Meng's actions and not realizing that danger was already approaching.
Lü Meng, relying on the strategy of "crossing the river in plain clothes," captured Jiangling City in one fell swoop. When the news reached the front lines at Fancheng, Guan Yu realized he had been tricked, filled with regret, and had no choice but to flee. At this point, Jingzhou once again fell under the sphere of influence of Eastern Wu. Sun Quan eliminated the threat posed by Guan Yu and gained control over the Yangtze River route, immediately strengthening his power.
The term "white robes crossing the river" does not refer to soldiers wearing white clothing, but rather to the act of removing armor, donning ordinary clothes, and secretly hiding elite troops in the ship's cabins to stealthily cross the Yangtze River. This was the most famous and successful surprise attack in the history of the Three Kingdoms period. If Guan Yu had not been so arrogant and underestimated his enemy, Lü Meng would not have been able to exploit the weakness, and this battle directly led to Guan Yu's defeat at Maicheng.