Empty Fort Strategy

The Empty Fort Strategy involves using reverse psychology to deceive the enemy into thinking that an empty location is full of traps and ambushes, and therefore induce the enemy to retreat. It is listed as the 32nd of the Thirty-Six Stratagems. Some examples are listed in the following sections.

According to the Sanguozhi, in 195, the Empty Fort Strategy was used by the warlord Cao Cao against his rival Lü Bu in one incident at Chengshi County (乘氏縣; southwest of present-day Juye County, Shandong). In the summer of that year, Lü Bu went to Dongmin County (東緡縣; northeast of present-day Jinxiang County, Shandong) and gathered about 10,000 troops to attack Cao Cao. At the time, Cao Cao had very few soldiers with him, but he set up an ambush and managed to defeat Lü Bu.

The Wei Shu (魏書) gave a more detailed account of the ambush. Cao Cao had sent most of his troops out to collect grain so he had less than 1,000 men available in his base, which could not be well defended with so few men. When Lü Bu showed up, Cao Cao ordered all his available soldiers to defend the base and even ordered women to stand guard on the walls. To the west of Cao Cao's base was a dyke, and to its south was a deep forest. Lü Bu suspected that there was an ambush, so he told his men, "Cao Cao is very cunning. We must not fall into his ambush." He then led his troops to 10 li (Chinese miles) south of Cao Cao's base and set up his camp there. The next day, Lü Bu came to attack Cao Cao, and by then, Cao Cao had really set up an ambush near the dyke with the soldiers that had returned from gathering the grain. Lü Bu's forces fell into the ambush and were defeated.

The "ambush" mentioned in the Sanguozhi refers to the ambush that Lü Bu's forces fell into a trap on the second day, as described in the Wei Shu. The incident is also mentioned in Sima Guang's Zizhi Tongjian. However, the Zizhi Tongjian account, which combined the Sanguozhi and Wei Shu accounts, did not mention the events on the first day – which were about Cao Cao sending all his available soldiers to defend the base and ordering women to stand guard on the walls.

Yi Zhongtian, a history professor from Xiamen University, commented on this incident in his book Pin San Guo (品三国) in response to criticism from Fudan University historian Zhou Zhenhe and an online commentator known as "Hongchayangweili" (红茶杨威利). Earlier on, Yi referred to this incident when he said in a lecture on the television programme Lecture Room that "Cao Cao's rights to the invention of the Empty Fort Strategy had been stolen from him". Zhou claimed that the Empty Fort Strategy had never been used in history before so there were no "rights" to its invention; the online commentator argued that the incident does not count as a use of the Empty Fort Strategy.

Yi defended his claim and said that the incident in 195 is valid because of the circumstances under which it was used, which were very similar to the incidents involving Zhao Yun and Wen Ping (see the sections below). Cao Cao was trying to confuse Lü Bu by making use of the geographical features (the "deep forest") and by ordering women to stand guard on the walls, so as to make Lü Bu suspect that he had set up an ambush in the "deep forest" and lure Lü Bu to attack his "weakly defended" base by deploying women as soldiers to show how "desperate" he was to set up a defence. The ploy worked because it made Lü Bu hesitate when he wanted to attack. Cao Cao had bought sufficient time to set up a real ambush, and he defeated Lü Bu when he came to attack again on the following day.

The Zhao Yun Biezhuan (趙雲別傳; Unofficial Biography of Zhao Yun) mentioned an incident about Zhao Yun, a general under the warlord Liu Bei, using the Empty Fort Strategy during the Battle of Han River in 219, fought between Liu Bei and his rival Cao Cao as part of the Hanzhong Campaign.

This incident took place after Cao Cao's general Xiahou Yuan was defeated and killed in action at the earlier Battle of Mount Dingjun. Cao Cao's forces were transporting food supplies to the north hill when Liu Bei's general Huang Zhong, heard about it and led a group of soldiers, including some of Zhao Yun's men, to seize the supplies. When Huang Zhong did not return after a long time, Zhao Yun led tens of horsemen in search of Huang. Zhao Yun's search party encountered Cao Cao's forces and engaged them in battle but were outnumbered and was forced to retreat back to camp with Cao Cao's men in pursuit. Zhao Yun's subordinate Zhang Yi wanted to close the gates of the camp to prevent the enemy from entering. However, Zhao Yun gave orders for the gates to be opened, all flags and banners to be hidden, and the war drums silenced. Cao Cao's forces thought that there was an ambush inside Zhao Yun's camp so they withdrew. Just then, Zhao Yun launched a counterattack and his men beat the war drums loudly and fired arrows at the enemy. Cao Cao's soldiers were shocked and thrown into disarray. Some of them trampled on each other while fleeing in panic, and many of them fell into the Han River in their haste to get away and drowned. When Liu Bei came to inspect the camp later, he praised Zhao Yun and held a banquet to celebrate his victory.