Battle of Hulao The Battle of Hulao ( 虎牢之戰 ) on 28 May 621 was a decisive victory for the Tang Dynasty prince Li Shimin , through which he was able to subdue two rival warlords , Dou Jiande and Wang Shichong . The battle was fought at the strategically important Hulao Pass , east of Luoyang . Li Shimin led a siege on the city of Luoyang , seat of the self - declared emperor Wang Shichong , who solicited help from Dou Jiande from the east . However , Dou Jiande delayed and when he finally arrived , Li Shimin brought forces to meet the new threat . Li Shimin ' s army avoided conflict until the troops of Dou Jiande were exhausted and then led a cavalry charge , breaking the opposing army and capturing Dou Jiande . Afterwards , Wang Shichong , seeing no other choice , surrendered Luoyang , and both his and Dou Jiande ' s states were absorbed by the Tang . Dou Jiande was later executed , resulting in some of his followers , led by Liu Heita , raising an unsuccessful rebellion against the Tang . Hulao marked the decisive turning point in the civil wars that followed the collapse of the Sui Dynasty , after which the eventual victory of the Tang was never in doubt . Background . During the later reign of the second emperor of the Sui Dynasty , Yang ( reigned 604 – 618 ) , the dynasty ' s authority began to wane : the immense material and human cost of the protracted and fruitless attempts to conquer the Korean kingdom of Goguryeo , coupled with natural disasters , caused unrest in the provinces , while the successive military failures eroded the emperor ' s prestige and legitimacy ( " Mandate of Heaven " ) among the provincial governors . Yang nevertheless continued to be fixated on the Korean campaigns , and by the time he realized the gravity of the situation , it was too late : as revolts spread , in 616 , he abandoned the north and withdrew to Jiangdu , where he remained until his assassination in 618 . Local governors and magnates rose to claim power in the wake of Yang ' s withdrawal . Nine major contenders emerged , some claiming the imperial title for themselves , others contenting themselves , for the time being , with more modest titles . Among the most well - positioned contenders was Li Yuan , Duke of Tang and governor of Taiyuan in the northwest ( modern Shanxi ) . A scion of a noble family related to the Sui dynasty , and with a distinguished career behind him , Li Yuan was an obvious candidate for the throne . His province possessed excellent natural defences , a heavily militarized population and was located near the capitals of Daxingcheng ( Chang ' an ) and Luoyang . In autumn 617 Li Yuan and his sons , Li Shimin and Li Jiancheng , led their troops south . In lightning campaign they defeated the Sui forces that tried to bar their way and , on 9 November , Li Yuan ' s troops stormed the capital . Li Yuan was now firmly placed as a major contender for the empire , and on 16 June 618 he proclaimed himself the first emperor of the Tang Dynasty . In a series of campaigns in 618 – 620 the Tang , led by the talented Li Shimin , soon managed to eliminate their rivals in the northwest and repulse Liu Wuzhou , who had taken control of Shanxi , but they still had to expand their control to the northeastern plain and the modern provinces of Hebei and Henan , which , in the words of H . Wechsler , would decide whether the new dynasty " would remain a regional regime or whether they would succeed in uniting the country under its control " . By early 620 , two major regimes had established themselves over this region . Henan was controlled by the Luoyang - based Wang Shichong , a former Sui general who declared himself the first emperor of the Zheng dynasty after defeating another rebel leader , Li Mi , at the Battle of Yanshi and absorbing his army and territories . Hebei was ruled by the one - time bandit leader Dou Jiande , who had risen in revolt already in 611 . From his base in central Hebei he had expanded his control south to the Yellow River , claiming the title of " King of Xia " . Like Wang and the Tang , he too made use of the Sui officialdom and administrative apparatus to maintain his realm . Li Shimin ' s campaign against Wang and Dou Jiande ' s march west . Fresh from his crushing victory over Liu Wuzhou , in August 620 Li Shimin , with an army of 50 , 000 men , began his advance from Shanxi towards Luoyang . His progress was swift : by September Tang troops had begun to establish a ring of fortified camps around the city , while detachments had penetrated further south , east and north , triggering the defection of most of central Henan from Wang ' s control . The monks of the nearby Shaolin Monastery also sided with Li Shimin , defeating a detachment of Wang ' s army at Mount Huanyuan and capturing his nephew , Wang Renze . Wang Shichong was now isolated in his capital and the territory immediately around it . The Tang were able to defeat his repeated attempts to break through the siege , and the supply situation in Luoyang grew steadily worse as the siege continued into winter and then spring . By March , people were reportedly shifting through dirt to find traces of food , or ate cakes of rice and mud . By this time , Wang ' s only hope for rescue was an intervention by Dou Jiande , to whom he had sent envoys already in late 620 . For Dou , the situation , as presented by his councillor Liu Bin , offered both danger and opportunity : if Luoyang fell , the Tang would next turn against Dou , but if Dou intervened and saved Luoyang , it would be easy to oust the weakened Wang and annex Henan to his own Xia state . It was therefore probably by design that Dou waited until April , when Wang ' s situation was critical , before he began marching west to relieve the siege of Luoyang . Dou ' s army was a huge force , reportedly over 100 , 000 strong , and the two earliest sources report 120 , 000 men . Although possibly exaggerated , an army of this size was well within the capabilities of the time . The Xia army was accompanied by a similarly large supply train , comprising both carts and boats . At the news of his approach , some of Li Shimin ' s generals suggested that he abandon the siege and retire west to Guanzhong , but the Tang prince refused to heed them . He left most of his army to maintain the siege , and with the rest he marched to the Hulao Pass , some to the east , which he occupied on 22 April . The Hulao Pass was formed by the ravine of the Sishui river . Lined on both banks by escarpments and steep hills , rising in the south to the Songshang mountains , it possessed major strategic importance — it has been described as a " Chinese Thermopylae " — as the east – west road along the Yellow River ' s south bank crossed it . Standoff at Hulao and Dou ' s strategic dilemma . When Dou ' s army arrived before the pass , it found the walled town and the western heights behind strongly held by the Tang . Dou encamped his forces at Banzhu , a plain east of the pass , and over the next weeks , repeatedly marched to Hulao and offered battle . Li Shimin , however , was content to remain in his powerful defensive position from which his numerically inferior force could easily hold the Xia at bay . The delay worked in his favour , as the continuing standoff only brought the garrison of Luoyang closer to starvation and surrender , and when this happened he would be able to launch his strike with the entire strength of the Tang army . Other passes were available through the hills near Hulao , but they were smaller and equally defensible ; given the size of the ZIa army , the only other alternatives would have been to bypass the Tang position entirely , either by crossing the Yellow River to the north or by venturing further south to the Huanyuan Pass . Indeed , one of Dou ' s civil officials , Ling Jing , suggested an alternative approach , namely to avoid any engagement with Li Shimin , cross to the northern bank of the Yellow River and strike at the Tang heartland in Shanxi , thereby both weakening the Tang and forcing them to abandon the siege of Luoyang without the Xia incurring any casualties . The plan was supported by Dou ' s wife , but was not adopted due to the vehement opposition of the Xia generals , who dismissed Ling Jing as an armchair general . Some sources also report that a number of the Xia generals had been bribed by Wang Shichong ' s agents . Whatever the true events , military historian D . Graff opines that logistical concerns played the major role in Dou ' s decision to stay at Banzhu , as his huge army was utterly dependent on proximity to the Yellow River and its canal network for its supplies . In addition , the heterogeneous nature of the Xia army , containing as it did the forces of various rebel leaders Dou had defeated over the past few years , and whose loyalty was doubtful , prevented Dou from dividing his army and sending various detachments on independent missions . Battle of Hulao Pass . In the event , after a month had passed , the Tang prince decided to force a confrontation . Li Shimin ' s reasons for this move are unknown ; D . Graff suggests that it is " possible that he believed the morale of Dou ' s men had deteriorated , and it is very likely that he did not wish to allow the exposed Xia army to withdraw to safety in Hebei after Luoyang had fallen " , or that he was frustrated at Luoyang ' s unexpectedly long resistance . At the same time , Li Shimin was evidently determined to exploit the opportunity offered by the tactical situation to score a crushing victory against Dou , which would result in the rapid absorption of his domains by the Tang . To entice his enemy to accept battle , Li Shimin sent his cavalry to raid Dou ' s supply lines , and positioned his troops at Hulao so as to suggest that only a small force was present . Dou took the bait , and on the early morning hours of 28 May led a large part of his army against Hulao , deploying his troops for battle along the eastern shore of the Sishui river . Per Li Shimin ' s plan , the Tang troops did not come forth to deploy for battle ; instead they remained in their strong defensive positions , waiting for the Xia army to tire and begin its withdrawal . Then the Tang , according to D . Graff , " would rush out and fall upon the by now demoralized and disorganized Xia army " . This conformed to Li Shimin ' s usual blueprint , which he had already employed to prevail over Xue Rengao and Liu Wuzhou : the Tang prince let the enemy advance , stretching their supply lines , and chose a suitable , highly defensible position where to confront them ; he avoided a direct confrontation , instead launching raids on his opponent ' s supply lines , awaiting either signs of weakness or the beginning of a retreat ; he then launched an all - out attack aiming at a crushing battlefield success , which he rendered decisive by following it up with a " relentless cavalry pursuit " , in D . Graff ' s words , to exploit it and bring about the collapse of his opponent ' s entire regime . Li Shimin ' s plan was successful : apart from skirmishes between the two armies ' cavalry , the two armies maintained their standoff from about 08 : 00 until noon , when the Xia troops began to show signs of thirst and weariness . Li Shimin , from a high vantage point , saw this and sent 300 cavalry in a probing attack . When he saw that the demoralized Xia recoiled from this assault , he sent more of his cavalry to turn Dou ' s left flank from the south . Dou reacted by ordering the withdrawal of his entire army from the river to the better defensive position offered by the eastern escarpment of the Sishui valley , but this manoeuvre created confusion in the Xia lines , breaking their battle order . Awaiting this opportunity , Li Shimin ordered his army to launch a general attack against the withdrawing Xia , himself spearheading the attack at the head of his remaining cavalry . Li Shimin always led from the front — accompanied by an elite force of 1000 black - clad , black - armoured horsemen — as indeed did most of the contemporary Chinese military leaders , who were expected to prove their personal bravery on the battlefield and motivate their men by their example , rather than stay in the rear and co - ordinate their army . The ensuing battle was bloody , but was decided when Li Shimin and a part of his cavalry broke through the Xia lines and reached the eastern escarpment , planting the Tang banners in full view of both armies . Possibly coupled with the arrival of the flanking Tang cavalry , this development caused the complete collapse of the Xia army : trapped between the Tang forces and the eastern cliffs , 3 , 000 Xia soldiers fell in the field or the subsequent pursuit , but more than 50 , 000 were taken prisoner . These included Dou Jiande himself , who was wounded and captured while trying to find a way to cross the Yellow River . Aftermath . The Tang victory at Hulao spelled the end for Luoyang too : bereft of any hope of rescue , Wang Shichong surrendered on 4 June , after Li Shimin displayed the captured Dou Jiande and his generals before the city walls . In stark contrast to the leniency with which the Tang treated most of their defeated rivals , Dou Jiande and Wang Shichong were soon eliminated : Dou was sent to Chang ' an , where he was executed , while Wang was ostensibly allowed to retire in exile , but was killed on his way there . Dou ' s wife and senior officials managed to escape the Xia camp and reach the safety of Hebei , but although some wanted to continue fighting under Dou ' s adopted son , most , including the influentian Qi Shanxinng , regarded the outcome of the battle as a sign that the Tang possessed the " Mandate of Heaven " , the divine right to rule . On 10 June , the Xia formally surrendered to the Tang , with Dou ' s ally Xu Yuanlang and Wang Shichong ' s brother Shibian following suit over the next days . As D . Graff writes , " the great victory at Hulao was the single most decisive engagement of the civil wars that separated the Sui collapse from the consolidation of Tang authority " . By defeating Dou Jiande and Wang Shichong , the Tang eliminated their two strongest rivals and brought the vital north - eastern plain under their control , thereby securing an unchallenged ascendancy over all other competing factions . Tang authority had not yet encompassed all of China , and new rebellions continued to occur for a few more years . The most notable of these occurred in late 621 , when the former Xia officials in Hebei rose up in reaction to the execution of Dou Jiande , under the leadership of Dou ' s cavalry commander Liu Heita . Nevertheless , the eventual outcome of the civil war had been decided at Hulao , and the various rebel leaders were overcome one by one . The last of them , Liang Shidu of Shuofang , was defeated in June 628 , marking the end of the civil war . In late 629 , Li Shimin , by now Emperor of China , ordered the erection of Buddhist monasteries on the sites of seven of the battles he had fought during the civil war . In a gesture that illustrated the emperor ' s desire to bridge and heal the divisions of the conflict , for Hulao he chose the name " Temple of Equality in Commiseration " .