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Shah Ala al-din Mohammed knew that killing emissaries was a violation of diplomatic custom. Perhaps he didn’t realize that killing Genghis Khan’s envoys amounted to suicide.

In 1218 Genghis Khan’s expanding Mongol empire came into direct contact with the Islamic world for the first time, specifically the central Asian kingdom of Khwarezm, which covered much of present-day Uzbekistan and Turkmenistan, as well as parts of Iran and Afghanistan. It also controlled the wealthy Silk Road cities of Samarkand, Bukhara, Urgench, Khojend, Merv and Nishapur. Although the population was predominantly Muslim, the country was riven with tribal and ethnic tensions. Warfare was incessant, and the army, a large part of it foreign mercenaries of Turkish origin, oppressed and terrorized the indigenous people. The shah of Khwarezm, Ala al-din Mohammed, was a violent and unstable libertine who the Persian chronicler Juvaini described as “constantly satisfying his desires in the company of fair songstresses and in continual drinking of purple wine.” The incompetence, arrogance and brutality of Mohammed’s rule, and more particularly his disastrous diplomatic response to the emerging Mongol power on his eastern border, would have dire consequences not only for his own kingdom but also for the whole Islamic world.

Genghis Khan had already established an excellent intelligence network among the mainly Muslim merchants who traveled the Silk Road. He was no doubt aware of the political situation in Khwarezm, and his ultimate strategic goal may well have been to exploit that instability. Initially, however, his stated aim was to establish mutually beneficial trade relations between the two empires. Commerce with their city-dwelling neighbors was essential to the nomad Mongol economy. Most of their clothing, for example, was acquired from these sources, and large amounts of grain were also imported into Mongolia.

At that time, the Mongols were in the process of subduing the Jurchens. Originally a nomadic tribe from Manchuria, the Jurchens had conquered a large slice of northeastern China and established themselves there as the Jin dynasty a century before. Mohammed was aware of the Mongol invasion and had heard tales concerning the savagery of Mongol armies from his own ambassador, who had arrived in the Jin capital of Zhongdu around 1215, soon after it had fallen to the Mongols. According to his emissary’s reports, the city was still surrounded by mountains of human bones and lakes of human fat. He also reported that 60,000 young women had thrown themselves from the city walls rather than fall into the hands of the invaders. The stories were exaggerated, but Mohammed believed them. Suspicious of Genghis’ true motives, he rejected the offer of peaceful commerce.

Genghis sent another message to the shah insisting that he wanted trade, not war. According to one source, he referred to Mohammed as “the best-loved of my sons.” The message was carried by a large delegation of merchants, all of whom were Muslim. Their brief, after delivering the conciliatory (if somewhat condescending) words of the Great Khan, was to initiate commercial contact with the Islamic kingdoms. Genghis’ intentions were possibly no more sinister than he had stated. Still in the process of subduing the Jin, he was unlikely to have wanted to deliberately involve himself in another conflict at the opposite end of his already sprawling empire.

When the merchants arrived in the Khwarezmid border city of Otrar in 1218, however, the governor, a relative of Mohammed’s, accused them of spying and had them arrested. It seems unlikely that this course of action would have been taken without Mohammed’s complicity. In a last-ditch attempt to avoid war, Genghis dispatched three emissaries, one Muslim and two Mongols, to Mohammed’s court with a request that the governor be handed over for appropriate punishment. The Mongol emissaries merely suffered the humiliation of having their beards shaved off before being sent back to Genghis. The Muslim envoy, on the other hand, was put to death. Mohammed then compounded this already unforgivable violation of diplomatic custom by ordering the imprisoned trade delegation executed as well.

When word of those atrocities reached Genghis, he vowed to avenge the murder of his ambassadors. Leaving a holding force in China to contain the Jurchens, who had been driven south after the loss of Zhongdu but remained undefeated, he turned the rest of his army westward to attack Khwarezm. There are conflicting reports as to the size of this army, but it could have numbered at most 200,000 men, and possibly as few as 90,000. Mohammed had a significantly larger force at his disposal—possibly as many as 400,000 soldiers—but due to his unpopularity, he was disinclined to place it under a single command structure for fear it would be turned against him. In addition, his ambassador to China had advised him that while the Mongols were invincible in open battle, they sometimes experienced difficulties when attempting to invest walled cities. Those two factors encouraged Mohammed to divide his army and garrison the components in the major cities of the kingdom, a strategy that was to greatly benefit the invading Mongols.

The Mongol military machine that marched on Khwarezm was in many ways fundamentally different from the one that the young Mongol Temujin had forged in the process of becoming Genghis Khan less than two decades before. While retaining the speed and flexibility of nomad cavalry, the traditional strengths of the steppe peoples, the Mongols had been introduced to the art of siegecraft in the course of their campaigns in China. They now had access to the most sophisticated techniques available at that time. Equipment such as battering rams, four-wheeled mobile shields, fire tubes, trebuchets and siege bows had become standard inclusions in the army’s baggage train. This never-before-seen combination of nomadic mobility and military technology would prove devastating, as Shah Mohammed was about to discover.

Predictably, the first city to draw the Mongols’ attention was Otrar, where the governor whose actions had instigated the war remained in command. The army reached the town in the fall of 1219, and Genghis assumed personal control of the attack, issuing strict orders that the governor was to be taken alive. After five months of siege, one of the city’s senior military leaders tried to flee through a side gate. He was captured and promptly executed by the Mongols, who then immediately forced entry into the city through the same gate. Otrar was quickly captured, and the governor retreated to the town’s citadel along with several hundred followers.

The citadel held out for another month, during which time the defenders, realizing they were doomed, launched wave after wave of suicidal charges against their besiegers. Finally, with all their missiles spent and most of his men dead, the governor and his remaining bodyguards retreated to the top floor of the fortress, where they were reduced to pelting their enemies with bricks and tiles. Despite this desperate last stand, the governor was captured alive as per the Great Khan’s orders. One source states that he was executed by having molten silver poured into his eyes and ears. The surviving inhabitants were led away into slavery, and the city itself was demolished. The destruction was so complete that Otrar never recovered, and the site remains uninhabited to the present day.

While the siege of Otrar was still in progress, Genghis sent his eldest son, Jochi, north along the Syr-Darya River toward the large city of Urgench, south of the Aral Sea. A small contingent of 5,000 men was sent south to reduce the city of Banakat. Leaving two other sons, Chaghatai and Ogodei, to mop up in Otrar, Genghis and his youngest son, Tolui, led a third army toward the wealthy trade centers of Bukhara and Samarkand.

Genghis had already discovered the effectiveness of terror as a component of war. Slaughtering the populations of cities that opposed him sent a clear message to their neighbors that resistance would not be tolerated. This brutal strategy conversely often resulted in the avoidance of unnecessary bloodshed. When the Mongol soldiers reached the town of Zarnuk, 200 kilometers north of Samarkand, tales of their savagery preceded them, and the citizens opened their gates without a fight. Staying only long enough to destroy the town’s citadel and draft a contingent of young men into his army, Genghis continued his march west, capturing the town of Nur before arriving outside the great city of Bukhara around February 1220.

Bukhara, with a population of about 300,000 and a history stretching back 500 years, almost rivaled Baghdad as a seat of Islamic culture and learning. It had a library of 45,000 books, some of the finest architecture in the Muslim world and was described by one chronicler as the “focus of splendor, the shrine of empire, the meeting-place of the most unique intellects of the age.”

Genghis immediately laid siege to the city. After three days the city garrison tried to break through the Mongol lines, and although a few managed to fight their way clear to the Amu-Darya River and safety, the majority (about 20,000 men by one account) were annihilated. The citizens of Bukhara, abandoned by their defenders, opened the gates.

A few hundred soldiers still remained barricaded in the citadel outside the town with their families. Genghis brought up his assault engines—mangonels, catapults and huge siege bows that could fire projectiles the size of telegraph poles—and started to batter the fortress. A large contingent of townspeople was assembled and driven toward the walls. The defenders were forced to respond by pouring burning naphtha down on their friends and neighbors, and the moat was soon filled with their corpses. It was a brave and desperate fight against overwhelming odds, but after 12 days the citadel was pounded into submission. The few male survivors “taller than the butt of a whip” were executed.

What followed was typical of the treatment afforded those who had the temerity to resist the Mongols. The inhabitants of Bukhara were ordered to leave the city with only the clothes on their backs. Any who were foolish enough to try to hide in their houses were rounded up and killed. The surviving population was divided into three groups: Artisans were deported to Mongolia, where they would continue to practice their craft for the benefit of the conquerors; men of fighting age were inducted into the army to be used as shock troops during subsequent battles; and the rest were distributed among the Mongol army as slaves. Genghis then let his soldiers loose on the deserted city and its helpless population. Bukhara was stripped of its assets, and its young women were raped. To compound the disaster, a fire broke out within the walls and the city, which apart from the mosques and palaces was constructed largely from wood. Bukhara, the “dome of Islam in the east,” was left a smoldering, desolate ruin. One account tells of Genghis Khan gathering the wealthier citizens together and delivering the following pronouncement from the pulpit of Bukhara’s main mosque: “I am the punishment of God. If you had not committed great sins, God would not have sent a punishment like me upon you.”

In March 1220, Genghis marched on Mohammed’s capital, Samarkand. Described as “the most delectable paradise of this world,” Samarkand was more heavily fortified than Bukhara, and its defenses had been further strengthened when news of the Mongol invasion had arrived. It also possessed a much larger garrison than Bukhara—as many as 100,000 troops by some accounts, although the numbers vary wildly from source to source. This is doubtless the reason Genghis captured the western city of Bukhara first before doubling back to attack Samarkand. The fall of its nearest neighbor would have been a blow to the city’s morale as well as ensuring there would be no reinforcements from that source.

Samarkand lies on the Zarafshan River in modern-day Uzbekistan. The Mongols approached the city along both banks of the river and surrounded it. By then, Genghis’ sons Ogodei and Chaghatai had completed the subjugation of Otrar and joined their father, along with their troops. Genghis ordered the prisoners from Bukhara forward, carrying battle standards to make his army appear even larger than it was. Those same hapless captives were subsequently placed in the vanguard of the initial assaults against the city walls and used as cannon fodder to absorb the brunt of the defense.

On the third day of the siege, Samarkand’s garrison launched a sortie. Employing their well-practiced tactic of feigned retreat, the Mongols lured them farther and farther from the protection of their walls before turning on the overextended enemy force and wiping it out. About 50,000 Khwarezmid soldiers died in that one engagement. Shah Mohammed tried to relieve Samarkand twice with cavalry, but neither force was able to break through the Mongol lines. After a siege that lasted only five days, the great city surrendered. The surviving members of the Turkish garrison, with the exception of 2,000 diehards who remained defiantly barricaded in the citadel, offered to join the Mongol army in exchange for clemency. Genghis accepted this offer, but only honored his promise until the last pocket of resistance was eliminated. He then had the entire garrison—approximately 30,000 men— put to death.

Perhaps the last straw for Mohammed was a forged letter Genghis arranged to have fall into his possession, containing a list of generals who were purportedly on the verge of betraying him. This well-timed piece of deception, coming as it did on top of the recent string of military disasters, was apparently too much for the shah, who fled westward. When this news reached Genghis, he sent two of his top generals, Jebe and Subedai, in pursuit with orders to track down and kill Mohammed.

With Samarkand captured, Genghis turned his attention toward the prosperous city of Urgench, located approximately 750 kilometers northwest of Bukhara, where the marshy delta of the Amu Darya River feeds into the Aral Sea. It was an important trade center and the nexus of several caravan routes. A network of canals provided irrigation, and a series of dikes protected the town from flooding. Mohammed’s mother, Terken Khatun, controlled the city. Genghis, aware there was still a substantial army in that part of Khwarezm, sent envoys to negotiate a surrender, assuring Terken that it was not her but her son against whom Genghis was waging war. At about the same time the emissaries arrived, Terken received the news that her son had fled and decided it would be prudent for her to do likewise. With several members of her family, she escaped westward, taking refuge in Mazandaran. But that fortress was soon captured and the whole family was sent to Genghis. He had the men executed and divided the women among his commanders. Terken Khatun was sent back to Mongolia and spent the rest of her life in captivity.

Meanwhile Jebe and Subedai continued their pursuit of Mohammed. In April 1220, they followed him across the Amu-Darya River into the province of Khurasan but lost the trail around the city of Nishapur. Mohammed continued his flight, reaching the shore of the Caspian Sea with his few remaining retainers, including his son Jalal ad-Din, around December 1220. Following the advice of some local emirs, he procured a boat and rowed to a small island in the Bay of Astrabad, where he died soon after. Some sources cite pneumonia as the cause of his death, but other writers have attributed it to the shock and despair of having so quickly and comprehensively lost his once great and wealthy empire.

With most of the royal family dead or in captivity, one of Mohammed’s generals, Khumar Tegin, seized control in Urgench, assuming the title of sultan. Genghis sent his sons Ogodei and Chaghatai to attack the city from the southeast while their elder brother Jochi, who had been campaigning along the Syr-Darya River, approached from the northeast. During the closing days of 1220, the jaws of this massive pincer movement closed.

The siege of Urgench would prove the most difficult in the whole campaign. Not only was the town well defended, it was surrounded by marshes, and there were no large stones available for the Mongols’ catapults. They improvised by chopping mulberry trees into projectile-size chunks and hurling them at the city walls. Prisoners were driven forward to fill in the moat and sap the walls, and after only a few days the invaders forced their way into the town. The inhabitants continued to resist bravely, defending their city street by street and house by house. Mongol tactics did not lend themselves to urban warfare of this kind, and they suffered greater losses than usual.

To further complicate matters, Jochi, who had been promised the city once it was captured, was eager to seize his prize in as pristine condition as possible and stopped the fighting several times to try negotiating a surrender. Those delays angered his brother Chaghatai and resulted in a serious rift between the two. When Genghis heard of their dispute, he appointed Ogodei commander, and the siege was resumed without further delay.

Urgench fell in April 1221. As usual, the artisans were sent to Mongolia and the young women and children enslaved. As punishment for resisting, the rest of the population was massacred. According to Juvaini, this task was assigned to 50,000 Mongol soldiers who were given the responsibility of executing 24 prisoners each. If this calculation is correct, the civilian death toll would have reached 1.2 million. Whether by coincidence or intent, the dike holding back the Amu-Darya River broke, and a large portion of the city was flooded, drowning many lucky enough to have survived the massacre.

While the siege of Urgench was still in progress, Genghis sent his youngest son Tolui across the Amu-Darya River to subdue the western province of Khurasan. Juvaini reports that Tolui’s force numbered only 7,000 men, but those Mongols were probably augmented by Turkish troops who, seeing the direction the war was taking, had begun deserting the crumbling Khwarezmid army in large numbers.

Tolui reached the city of Merv in February 1221. Merv, locally known as the “Queen of Cities,” had existed since the 7th century BC and at the time of the Mongol invasion was one of the most important cultural centers in the eastern Muslim world. Its 10 libraries were said to contain 150,000 books, and it was in the tower of the city’s observatory that the great poet and astronomer Omar Khayyam compiled his renowned astronomical tables. Juvaini described Merv in the following terms: “In extent of territory it excelled among the lands of Khurasan, and the bird of peace and security flew over its confines. The number of its chief men rivaled the drops of April rain, and its earth contended with the heavens.”

Merv’s garrison comprised 12,000 men, and the city’s population, normally 70,000, had swollen to 10 times that number due to the influx of terrified refugees seeking protection from the Mongols. Tolui rode around the city for six days, becoming familiar with its outworks, walls and moats, then on the seventh day launched an assault against the town’s Shahristan Gate. The defenders responded with a sortie but were soon beaten back. The Mongols failed to break into the city, however, and took up positions in a series of rings around the beleaguered fortress.

The next day Merv’s governor, Mujir-al-Mulk, believing his position was untenable, offered to surrender the city on the proviso that the lives of its people were spared. Unfortunately for Merv, they were facing arguably the most bloodthirsty and vicious of Genghis Khan’s offspring. Tolui agreed to the terms to hasten the end of the siege, but went back on his word as soon as the city had been handed over. The entire population was herded into the plain outside the city walls. A small contingent of 400 artisans and some of the city’s younger children were marched away into slavery. The rest of the population was slaughtered.

Juvaini reported that every Mongol soldier “was allotted the execution of three or four hundred persons” and added, “So many had been killed by nightfall that the mountains became hillocks and the plain was soaked with the blood of the mighty.” A contemporary tally, conducted over a period of 13 days, arrived at a staggering figure of 1.3 million dead.

From Merv, Tolui continued his march west, reaching the large city of Nishapur in April 1221. In November of the previous year, Tolui’s brother-in-law Toquchar had been killed during an unsuccessful assault on the town, and Tolui was bent on revenge. When Nishapur fell after only three days, he ordered the entire population massacred. Even the cats and dogs were not spared. The city was so thoroughly dismantled that the ground where it had stood could not be plowed. Heart, the last settlement of any significance left in the area, wisely chose to surrender without a fight. Tolui returned to his father’s camp at Talaqan to report that he had successfully completed his mission; the province of Khurasan with its well-defended cities and substantial armies had been completely subjugated in less than three months.

Shah Mohammed’s son, Jalal ad-Din, was still at large. He rallied the remnants of his father’s once great army and retreated south into present-day Afghanistan. In the spring of 1221, he engaged the force pursuing him near the town of Parwan, inflicting on it the first and only major defeat the Mongols suffered in the entire campaign. When the news of that battle’s outcome reached Genghis, he marched south with his own army and trapped Jalal on the banks of the Indus River. The Khwarezmids put up a brave defense but were overwhelmed. Jalal managed to escape across the Indus, but Genghis, recognizing that he no longer posed a threat, declined to pursue him. With Jalal ad-Din gone, all organized resistance to the Mongols ceased, and the greatest power in central Asia was absorbed into the Mongol empire.

Juvaini certainly exaggerated the level of destruction inflicted on Khwarezm during the Mongols’ two-year campaign. His figure of 2.5 million killed during and immediately after the sieges of Urgench and Merv alone seem impossible when contemporary estimates indicate that the entire population of the empire at that time was not much more than 3 million people. For example, it seems unlikely that Bukhara, after being subjected to the level of destruction that Juvaini reported, could be described only 40 years later as a flourishing and wealthy metropolis.

Nevertheless, the westward expansion of the Mongol empire was undoubtedly a catastrophe for the Islamic world in general, and Khwarezm in particular. The archaeological evidence confirms this. As Juvaini said, “With one stroke a world which billowed with fertility was laid desolate, and the regions thereof became a desert and the greater part of the living dead and their skins and bones crumbling dust; and the mighty were humbled and immersed in the calamities of perdition.”


Kim Stubbs is an Australian freelance writer specializing in ancient and early medieval history. For further reading, he recommends: Genghis Khan: Conqueror of the World, by Leo de Hartog; and Genghis Khan, by Michel Hoang, translated by Ingrid Cranfield.

Originally published in the May 2006 issue of Military History. To subscribe, click here