if he submitted. By late 208, with help from Zhou Yu, Lu Su, and Zhuge Liang (who represented Liu Bei in the diplomatic exchange), an alliance was formed between Sun Quan and Liu Bei against Cao Cao. Battle of Red Cliffs (208) Sun Quan put Zhou Yu in command of his 30,000 troops, largely stationed on naval vessels. Zhou Yu set up a defensive position in conjunction with Liu Bei, whose army garrisoned on land. Around this time, a spreading plague significantly weakened Cao Cao's forces. Zhou Yu's subordinate Huang Gai pretended to defect to Cao Cao's side and was accepted by the latter. Huang Gai brought a small group of men with him and sailed towards Cao Cao's base on boats. As the boats approached Cao Cao's fleet, Huang Gai ordered his men to set the boats on fire, and the burning boats crashed into Cao Cao's larger ships. The fire spread out of control and destroyed Cao Cao's entire naval fleet. Cao Cao's land forces at Wulin (烏林; in present-day Honghu, Hubei) were also attacked and driven back by Sun Quan and Liu Bei's armies. Cao Cao suffered a drastic defeat at the Battle of Red Cliffs and was forced to retreat north back to Jiangling (江陵, located in present-day Jingjiang 荆江, not to be confused with present-day Jiangling County, Hubei). Emergence of the Three Kingdoms (209–220) Sun–Liu conquest of Jing Province (209–210) Immediately after the Battle of Red Cliffs, Sun Quan's forces under Zhou Yu's command pressed on another attack on Cao Cao, leading to the Battle of Jiangling. On the other hand, Liu Bei used the opportunity to attack the four commanderies of Wuling, Changsha, Lingling and Guiyang in southern Jing Province and bring them under his control. By early 209, Cao Cao had lost most of Jing Province to the allies. As Liu Bei had become relatively more powerful after his conquests of the four commanderies, Sun Quan became apprehensive of him and decided to strengthen their alliance by arranging for a marriage between his younger sister, Lady Sun, and Liu Bei. Zhou Yu was suspicious of Liu Bei's intentions and suggested to Sun Quan to capture Liu Bei, put him under house arrest, and then take control over Liu's forces. However, Sun Quan rejected Zhou Yu's idea as he believed that Liu Bei's forces would rebel against him even if the plan succeeded. Sun