Empty Fort Strategy

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

Empty Fort Strategy
Zhuge Liang against Sima Yi with his sons Sima Zhao and Sima Shi, as depicted in the artwork Ruse with an Empty City
Traditional Chinese空城計
Simplified Chinese空城计

Cao Cao

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.[1]

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.[2]

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.[3]

Debate

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.[4]

Zhao Yun

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.[5]

Wen Ping

The Weilüe mentioned an incident about the Empty Fort Strategy being used by a general Wen Ping during a battle between the forces of the states of Cao Wei and Eastern Wu in the Three Kingdoms period. It is not clear which battle this was, but it could have been the Battle of Jiangling of 223.

The Wu leader Sun Quan led thousands of troops to attack a fortress defended by the Wei general Wen Ping. At the time, there were heavy rains and many fortifications were damaged. The civilians in the fortress had retreated to the fields further back so they could not help with repairs to the fortifications, and some repairs were still uncompleted when Sun Quan arrived with his men. When Wen Ping heard that Sun Quan had arrived, he was unsure of what to do, but eventually formulated a plan to deceive him. He ordered everyone in the fortress to stay under cover while he hid behind the walls, creating an illusion of an empty fortress. As Wen Ping expected, Sun Quan became suspicious and he said to his subordinates, "The northerners regard this man (Wen Ping) as a loyal subject, which is why they entrusted him with defending this commandery. Now, as I approach, he does not make any move. It must be either that he has something up his sleeve or that his reinforcements have arrived." Sun Quan then withdrew his forces.[6]

The historian Pei Songzhi commented that the Weilüe account did not match the original account in the Sanguozhi. The Sanguozhi mentioned: "Sun Quan led 50,000 troops to besiege Wen Ping at Shiyang (石陽). The situation was very critical but Wen Ping put up a firm defence. Sun Quan withdrew his forces after more than 20 days, and Wen Ping led his men to attack them as they were retreating and defeated them."[7]

Zhuge Liang
Wooden sculptures of Sima Yi's army fleeing from an old man sweeping in front of an empty city, in Huaxilou, Bozhou, Anhui

One of the best known examples of the use of the Empty Fort Strategy is a fictional incident in the novel Romance of the Three Kingdoms, which romanticises historical events in the late Han dynasty and the Three Kingdoms period. This event took place during the first of a series of campaigns – known as Zhuge Liang's Northern Expeditions – led by Shu Han's chancellor Zhuge Liang to attack Shu's rival state, Cao Wei.

In the first Northern Expedition, Zhuge Liang's efforts to conquer the Wei city Chang'an were undermined by the Shu defeat at the Battle of Jieting. With the loss of Jieting (present-day Qin'an County, Gansu), Zhuge Liang's current location, Xicheng (西城; believed to be located 120 li southwest of present-day Tianshui, Gansu), became exposed and was in danger of being attacked by the Wei army. In the face of imminent danger, with the main Shu army deployed elsewhere and only a small group of soldiers in Xicheng with him, Zhuge Liang came up with a ploy to hold off the approaching enemy.

Zhuge Liang ordered all the gates to be opened and instructed soldiers disguised as civilians to sweep the roads while he sat on the viewing platform above the gates with two page boys by his side. He put on a calm and composed image by playing his guqin. When the Wei army led by Sima Yi arrived, Sima was surprised by the sight before him and he ordered a retreat after suspecting that there was an ambush inside the city. Zhuge Liang later explained that his strategy was a risky one. It worked because Zhuge Liang had a reputation for being a careful military tactician who hardly took risks, so Sima Yi came to the conclusion that there was certainly an ambush upon seeing Zhuge's relaxed composure.[8]

As a topic of academic study

Christopher Cotton, an economist from the Queen's University, and Chang Liu, a graduate student, used game theory to model the bluffing strategies used in the Chinese military legends of Li Guang and his 100 horsemen (144 BC), and Zhuge Liang and the Empty City (228 AD). In the case of these military legends, the researchers found that bluffing arose naturally as the optimal strategy in each situation. The findings were published under the title 100 Horsemen and the empty city: A game theoretic examination of deception in Chinese military legend in the Journal of Peace Research in 2011.[9][10]

Historicity

The basis for this story in Romance of the Three Kingdoms is an anecdote shared by one Guo Chong (郭沖) in the early Jin dynasty (266–420).[11] In the fifth century, Pei Songzhi added the anecdote as an annotation to Zhuge Liang's biography in the third-century historical text Sanguozhi. The anecdote is as follows:

Zhuge Liang garrisoned at Yangping (陽平; around present-day Hanzhong, Shaanxi) and ordered Wei Yan to lead the troops east. He left behind only 10,000 men to defend Yangping. Sima Yi led 200,000 troops to attack Zhuge Liang and he took a shortcut, bypassing Wei Yan's army and arriving at a place 60 li away from Zhuge Liang's location. Upon inspection, Sima Yi realised that Zhuge Liang's city was weakly defended. Zhuge Liang knew that Sima Yi was near, so he thought of recalling Wei Yan's army back to counter Sima Yi, but it was too late already and his men were worried and terrified. Zhuge Liang remained calm and instructed his men to hide all flags and banners and silence the war drums. He then ordered all the gates to be opened and told his men to sweep and dust the ground. Sima Yi knew that impression that Zhuge Liang was a cautious and prudent man, and he was baffled by the sight before him and suspected that there was an ambush. He then withdrew his troops. The following day, Zhuge Liang clapped his hands, laughed, and told an aide that Sima Yi thought that there was an ambush and had withdrawn. Later, his scouts returned and reported that Sima Yi had indeed retreated. Sima Yi was very upset when he later found out about the ruse.[12]

After adding the anecdote to Zhuge Liang's biography, Pei Songzhi wrote a short commentary as follows:

When Zhuge Liang garrisoned at Yangping, Sima Yi was serving as the Area Commander of Jing Province and he was stationed at Wancheng (宛城; present-day Wancheng District, Nanyang, Henan). He only came into confrontation with Zhuge Liang in Guanzhong after Cao Zhen's death (in 231). It was unlikely that the Wei government ordered Sima Yi to lead an army from Wancheng to attack Shu via Xicheng (西城; present-day Ankang, Shaanxi) because there were heavy rains at the time (which obstructed passage). There were no battles fought at Yangping before and after that period of time. Going by Guo Chong's anecdote, if Sima Yi did lead 200,000 troops to attack Zhuge Liang, knew that Zhuge Liang's position was weakly defended, and suspected that there was an ambush, he could have ordered his troops to surround Zhuge Liang's position instead of retreating. Wei Yan's biography mentioned: "Each time Wei Yan followed Zhuge Liang to battle, he would request to command a separate detachment of about 10,000 men and take a different route and rendezvous with Zhuge Liang's main force at Tong Pass. Zhuge Liang rejected the plan, and Wei Yan felt that Zhuge Liang was a coward and complained that his talent was not put to good use." As mentioned in Wei Yan's biography, Zhuge Liang never agreed to allow Wei Yan to command a separate detachment of thousands of troops. If Guo Chong's anecdote was true, how was it possible that Zhuge Liang would allow Wei Yan to lead a larger army ahead while he followed behind with a smaller army? Guo Chong's anecdote was endorsed by the Prince of Fufeng (Sima Jun, a son of Sima Yi). However, the story puts Sima Yi in a negative light, and it does not make sense for a son to approve a story which demeans his father. We can tell that this anecdote is fake after reading the sentence "the Prince of Fufeng endorsed Guo Chong's anecdote".[13]

Evidence from historical sources indicate that Sima Yi was indeed not in Jieting at the time. The Battle of Jieting took place in 228 but Sima Yi's biography in the Book of Jin claimed that in 227, Sima Yi was stationed at Wancheng in the north of Jing Province. He led an army to suppress a rebellion by Meng Da at Xincheng (新城; in present-day northwestern Hubei), and returned to Wancheng after his victory. Later, he went to the imperial capital Luoyang to meet the Wei emperor Cao Rui, who consulted him on some affairs before ordering him to return to Wancheng.[14] Sima Yi only engaged Zhuge Liang in battle after 230.[15]

Yi Zhongtian, a professor from Xiamen University, commented on this incident in his book Pin San Guo (品三国). He pointed out three problems in the story:[4]

  1. Sima Yi did not dare to attack because he feared that there was an ambush inside the fortress. If so, he could have sent recces to scout ahead and check if there was really an ambush.
  2. Romance of the Three Kingdoms provided this description: "(Sima Yi) saw Zhuge Liang sitting at the top of the gates, smiling and playing his guqin and being oblivious to his surroundings."[16] Based on this description, the distance between Sima Yi and Zhuge Liang must have been very short, or else Sima would not have been able to observe Zhuge's actions so clearly. If so, Sima Yi could have ordered an archer to kill Zhuge Liang.
  3. Both Guo Chong's anecdote and Romance of the Three Kingdoms said that Sima Yi's army was superior to Zhuge Liang's in terms of size: Guo Chong's anecdote stated that Sima Yi had 200,000 men while Zhuge Liang had 10,000 men; Romance of the Three Kingdoms mentioned that Sima Yi had 150,000 men while Zhuge Liang had only 2,500 men.[17] If so, Sima Yi could have ordered his troops to surround Zhuge Liang's fortress first, and then wait for an opportunity to attack.

Li Yuan

According to historical sources such as the Old Book of Tang, New Book of Tang and Zizhi Tongjian, Li Yuan, the founding emperor of the Tang dynasty, used a similar strategy in 618 CE in a battle against the Turks before he started his rebellion against the Sui dynasty. In early 618, Li Yuan was still a Sui general and his base was Jinyang (晉陽; present-day Taiyuan, Shanxi). When he heard rumours that Emperor Yang wanted to execute him, he started making preparations for a rebellion against the Sui dynasty to save himself. In May 618, the Turks allied with the warlord Liu Wuzhuo to attack the Sui dynasty in order to gain territory. Jinyang became one of their targets.

Around the time, Li Yuan had just arrested Wang Wei (王威) and Gao Junya (高君雅), two officials sent by Emperor Yang to spy on him. He was also still busy plotting his rebellion.[18] Moreover, he was also not prepared for a battle against the Turks because of two reasons. Firstly, the Turk cavalry was so powerful that Li Yuan was not confident that his troops could defeat the enemy. Secondly, even if Li Yuan won the battle, he would nonetheless suffer significant losses that would undermine his rebellion against the Sui dynasty.

Li Yuan thus ordered his soldiers to hide in Jinyang and leave the city gates wide open. Shibi Khan, who led the Turk cavalry, saw that the city appeared to be deserted and feared that there might be an ambush, so he did not enter. Li Yuan then ordered his son Li Shimin and subordinate Pei Ji to make their troops beat war drums loudly in the empty camps they had set up earlier, so as to create an illusion that reinforcements had arrived in Jinyang. Shibi Khan was so frightened that he retreated after two days.[19]

Battle of Mikatagahara

Many traditions say that in 1572, during the Sengoku Period in Japan, Tokugawa Ieyasu used the tactic during his retreat in the Battle of Mikatagahara. He commanded that the fortress gates remain open, and that braziers be lit to guide his retreating army back to safety. One officer beat a large war drum, seeking to add encouragement to the returning men of a noble, courageous retreat. When the enemy forces, led by Baba Nobuharu and Yamagata Masakage heard the drums, and saw the braziers and open gates, they assumed that Tokugawa was planning a trap, and so they stopped and made camp for the night. The authenticity of this story has been disputed by some, however, as it appears to be copied straight from Zhuge Liang's story, perhaps in an attempt to embellish Tokugawa's career.[20]

References
  1. (二年春，襲定陶。濟陰太守吳資保南城，未拔。會呂布至，又擊破之。夏，布將薛蘭、李封屯钜野，太祖攻之，布救蘭，蘭敗，布走，遂斬蘭等。布複從東緡與陳宮將萬餘人來戰，時太祖兵少，設伏，縱奇兵擊，大破之。布夜走，太祖複攻，拔定陶，分兵平諸縣。) Sanguozhi vol. 1.
  2. (魏書曰：於是兵皆出取麥，在者不能千人，屯營不固。太祖乃令婦人守陴，悉兵拒之。屯西有大堤，其南樹木幽深。布疑有伏，乃相謂曰：“曹操多譎，勿入伏中。”引軍屯南十餘裏。明日複來，太祖隱兵堤裏，出半兵堤外。布益進，乃令輕兵挑戰，既合，伏兵乃悉乘堤，步騎並進，大破之，獲其鼓車，追至其營而還。) Wei Shu annotation in Sanguozhi vol. 1.
  3. (布復從東緡與陳宮將萬餘人來戰，操兵皆出收麥，在者不能千人，屯營不固。屯西有大堤，其南樹木幽深，操隱兵堤裡，出半兵堤外。布益進，乃令輕兵挑戰，既合，伏兵乃悉乘堤，步騎並〔進〕(追)，大破之，追至其營而還。布夜走，操復攻拔定陶，分兵平諸縣。) Zizhi Tongjian vol. 61.
  4. Yi, Zhongtian (2006). Huang, Tingting (ed.). 品三國 [Pin San Guo] (in Chinese). Hong Kong: Joint Publishing (H.K.) Co., Ltd. pp. 367–372. ISBN 978-962-04-2609-4.
  5. (夏侯淵敗，曹公爭漢中地，運米北山下，數千萬囊。黃忠以為可取，雲兵隨忠取米。忠過期不還，雲將數十騎輕行出圍，迎視忠等。值曹公揚兵大出，雲為公前鋒所擊，方戰，其大眾至，勢偪，遂前突其陳，且鬥且卻。公軍散，已復合，雲陷敵，還趣圍。將張著被創，雲復馳馬還營迎著。公軍追至圍，此時沔陽長張翼在雲圍內，翼欲閉門拒守，而雲入營，更大開門，偃旗息鼓。公軍疑雲有伏兵，引去。雲雷鼓震天，惟以戎弩於後射公軍，公軍驚駭，自相蹂踐，墮漢水中死者甚多。先主明旦自來至雲營圍視昨戰處，曰：「子龍一身都是膽也。」作樂飲宴至暝，軍中號雲為虎威將軍。) Zhao Yun Biezhuan annotation in Sanguozhi vol. 36.
  6. (魏略曰：孫權嘗自將數萬眾卒至。時大雨，城柵崩壞，人民散在田野，未及補治。聘聞權到，不知所施，乃思惟莫若潛默可以疑之。乃敕城中人使不得見，又自臥舍中不起。權果疑之，語其部黨曰：「北方以此人忠臣也，故委之以此郡，今我至而不動，此不有密圖，必當有外救。」遂不敢攻而去。魏略此語，與本傳反。) Weilüe annotation in Sanguozhi vol. 18.
  7. (孫權以五萬眾自圍聘於石陽，甚急，聘堅守不動，權住二十餘日乃解去。聘追擊破之。) Sanguozhi vol. 18.
  8. Sanguo Yanyi ch. 95-96.
  9. The full reference of the work is: C. Cotton; C. Liu. 100 Horsemen and the empty city: A game theoretic examination of deception in Chinese military legend. Journal of Peace Research, 2011; 48 (2): 217 DOI: 10.1177/0022343310396265.
  10. "To bluff, or not to bluff? Modern-day game theory techniques sheds light on legendary military bluffs". Science Daily. 29 March 2012. Retrieved 12 February 2013. reprinted from materials provided by University of Miami
  11. (蜀記曰：晉初，扶風王駿鎮關中，司馬高平劉寶、長史熒陽桓隰諸官屬士大夫共論諸葛亮，于時譚者多譏亮託身非所，勞困蜀民，力小謀大，不能度德量力。金城郭沖以為亮權智英略，有踰管、晏，功業未濟，論者惑焉，條亮五事隱沒不聞於世者，寶等亦不能復難。扶風王慨然善冲之言。) Shu Ji annotation in Sanguozhi vol. 35.
  12. (亮屯於陽平，遣魏延諸軍並兵東下，亮惟留萬人守城。晉宣帝率二十萬眾拒亮，而與延軍錯道，徑至前，當亮六十里所，偵候白宣帝說亮在城中兵少力弱。亮亦知宣帝垂至，已與相偪，欲前赴延軍，相去又遠，回跡反追，勢不相及，將士失色，莫知其計。亮意氣自若，敕軍中皆臥旗息鼓，不得妄出菴幔，又令大開四城門，埽地卻灑。宣帝常謂亮持重，而猥見勢弱，疑其有伏兵，於是引軍北趣山。明日食時，亮謂參佐拊手大笑曰：「司馬懿必謂吾怯，將有彊伏，循山走矣。」候邏還白，如亮所言。宣帝後知，深以為恨。) San Shi annotation in Sanguozhi vol. 35.
  13. (難曰：案陽平在漢中。亮初屯陽平，宣帝尚為荊州都督，鎮宛城，至曹真死後，始與亮於關中相抗禦耳。魏嘗遣宣帝自宛由西城伐蜀，值霖雨，不果。此之前後，無復有於陽平交兵事。就如沖言，宣帝既舉二十萬眾，已知亮兵少力弱，若疑其有伏兵，正可設防持重，何至便走乎？案魏延傳云：「延每隨亮出，輒欲請精兵萬人，與亮異道會於潼關，亮制而不許；延常謂亮為怯，歎己才用之不盡也。」亮尚不以延為萬人別統，豈得如沖言，頓使將重兵在前，而以輕弱自守乎？且沖與扶風王言，顯彰宣帝之短，對子毀父，理所不容，而雲「扶風王慨然善沖之言」，故知此書舉引皆虛。) Pei Songzhi's annotation in Sanguozhi vol. 35.
  14. (太和元年六月，天子詔帝屯於宛，加督荊、豫二州諸軍事。 ... 天子並然之，複命屯於宛。) Jin Shu vol. 1.
  15. ([太和]四年，遷大將軍，加大都督、假黃鉞，與曹真伐蜀。) Jin Shu vol. 1.
  16. (果見孔明坐於城樓之上，笑容可掬，傍若無人焚香操琴。) Sanguo Yanyi ch. 95.
  17. (忽然十餘次飛馬報到，說司馬懿引大軍十五萬，望西城蜂擁而來。時孔明身邊並無大將，只有一班文官，所引五千軍，已分一半先運糧草去了，只剩二千五百軍在城中。) Sanguo Yanyi ch. 95.
  18. (副留守虎賁郎將王威、虎牙郎將高君雅見兵大集，疑有變，謀因禱雨晉祠以圖高祖。高祖覺之，乃陰為備。五月甲子，高祖及威、君雅視事，開陽府司馬劉政會告威、君雅反，即坐上執之。丙寅，突厥犯邊，高祖令軍中曰：「人告威、君雅召突厥，今其果然。」遂殺之以起兵。) Xin Tang Shu vol. 1.
  19. (時世民已布兵塞衢路，文靜因與劉弘基、長孫順德等共執威、君雅繫獄。丙寅，突厥數萬衆寇晉陽，輕騎入外郭北門，出其東門。淵命裴寂等勒兵為備，而悉開諸城門，突厥不能測，莫敢進。衆以為威、君雅實召之也，淵於是斬威、君雅以徇。淵部將王康達將千餘人出戰，皆死，城中忷懼。淵夜遣軍潛出城，旦則張旗鳴鼓自他道來，如援軍者；突厥終疑之，留城外二日，大掠而去。) Zizhi Tongjian vol. 183.
  20. Turnbull, Stephen R. (2000). The samurai sourcebook. London: Cassell. ISBN 1854095234. OCLC 44910809.
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