In November 1257, unconvinced of the Caliph’s power to speak for either God or the entire Muslim population, Hulegu began to march toward Baghdad. He approached more cautiously than his grandfather would have done, but nevertheless with the same set of proven Mongol strategies and tactics. To supplement his own army, Hulegu summoned the armies of the vassal states of Armenia and Georgia, as well as a variety of Turkic tribes. Thus, while the main army approached in a wide arc from the north and the east, the others approached from the north and west. Although the Tigris and Euphrates Rivers had historically served as natural barriers to foreign attacks on Mesopotamia, the Mongols easily moved back and forth across the rivers with a series of pontoon boats. As the invading armies advanced, they set the local population to flight toward the safety of the fortified city. By the final week of January 1258, the invading armies had encircled the city and occupied the extensive suburbs beyond the city walls, filling the city to its maximum with refugees.
Before commencing the attack, Hulegu sought to exploit political, religious, and ethnic divisions within Baghdad by forging secret ties to the Christians within the city. Because his mother and his two wives were Christians, as well as many of his own men, Hulegu cultivated contacts and nourished respect within the Christian communities across the Middle East, and he had maintained good relations with his Christian vassal kingdoms, Georgia and Armenia. Taking advantage of these connections, Christian envoys secretly slipped back and forth between the city and the Mongol camp, bringing vital reconnaissance to Hulegu and carrying back promises of special treatment to the Christians and other minorities in the city. As a sign of the special favor that the Christians would enjoy under his rule, Hulegu exempted Christian priests from kowtowing at court, since they bowed only to God. Hulegu exploited the fears of the Christians of Baghdad as a small minority in a sea of potentially hostile Muslims. He fed the dreams of Christians and Jews of finally freeing themselves from Muslim domination.
The Caliph also tried to use to his own benefit the close ties of the Mongols and the Christians. He summoned the Catholikos Makikha, the patriarch of the Christian church, and dispatched him and a Muslim minister to negotiate with the Mongols. He offered to make a formal submission, pay enormous tribute, and to read Friday prayers in the mosque in the name of the Great Khan, thereby officially acknowledging his subservience to Mongol rule. Hulegu scoffed at the offer. He knew that he was already too close to victory to settle for such trifles—not when all the wealth of the richest city on earth could easily be his.
The Mongols showed their traditional ability to improvise and use whatever material presented itself as a possible weapon. The largest objects in the vicinity were the tall date palm trees that the Arabs had cultivated and nourished for centuries. The Mongols chopped them down, and turned the trunks into lethal missiles that they fired at the city. Lacking sufficient wood to encircle the large city of Baghdad as the Mongols had done with the cities of Russia, Hulegu nevertheless surrounded the city with a deep ditch and a rampart and began the assault with a terrifying bombardment of the city. The Arabs knew of the use of flamethrowers in combat, but until this point had not encountered the military power of gunpowder.
The Mongols had changed the formula of gunpowder to provide enough oxygen to make it ignite in one rapid blast rather than in the traditional slow burn of the firelance or of rockets. Such instantaneous burning produced an explosion rather than a fire, and the Mongols harnessed these explosions to hurl a variety of projectiles. Craftsmen made some of the tubes small enough that a single man could operate them and thus fire out arrowheads or other metal projectiles. The explosion in these tubes required a stronger material than bamboo; so they were made with iron tubes. The Mongols attached the smaller tubes to a wooden handle for ease of handling, and they mounted the larger ones on wheels for ease of mobility. Larger tubes fired ceramic or metal cases filled with shrapnel or more gunpowder that produced a secondary explosion upon impact. In their assault, the Mongols combined all of these forms of bombardment in an assortment of smoke bombs, proto-grenades, simple forms of mortars, and incendiary rockets. They had developed explosive devices able to hurl projectiles with such force that they may as well have been using real cannons; they managed to concentrate their fire on one area of the city defenses and hammer it down.
The bombardment from such a distance confused and frightened the residents of Baghdad and frustrated its defenders, who had never before been attacked by an enemy too far away to be reached by their weapons. In addition to the gunpowder weapons, Mongol engineers had nearly perfected the use of planted explosives to undermine walls. All of these military innovations complied with the strong Mongol preference to stay as far from the actual fighting and killing as possible. Hulegu destroyed the dams and diverted the Tigris to flood the camp of the Caliph’s army and make them take refuge in the city. The wall of water surrounding the city must have had a similar psychological impact on the people of Baghdad as the wooden wall had produced on the people of the Russian cities. On February 5, 1258, the Mongol forces broke through the walls of Baghdad, and after five days, the Caliph capitulated. To prepare the city for looting, Hulegu ordered the people of Baghdad to surrender their weapons, leave all their goods, and march out of the city. Rather than comply with the order, the defending army bolted and tried to escape, but the Mongols gave chase and cut them down.
Hulegu sent his Christian troops into the city to collect the loot, but they found many people had refused the order to evacuate and were still hiding in their homes. For disobeying the order, the invaders killed them. By Mongol order, the churches and Christian property in the city remained secure from plunder, and Hulegu presented one of the Caliph’s palaces to the Catholikos Makikha. The Christians inside Baghdad joined their fellow believers to loot the city and slaughter the Muslims, from whom they felt their salvation had finally come. Centuries of hatred and anger spilled out as they defiled and destroyed mosques, and turned many of them into churches. The Christians celebrated joyously throughout the Abbasid lands and beyond. An Armenian chronicler described the exulting joy: “Five hundred and fifteen years have passed since the founding of the city,” he wrote. “Throughout its supremacy, like an insatiable leech it [Baghdad] had swallowed up the entire world. Now it restored all that had been taken.” Now Baghdad “was punished for the blood it had shed and the evil it had done; the measure of its iniquity was full.” The looting lasted seventeen days. During this time, the invaders, accidentally or deliberately, set the city afire.
Hulegu allowed the Christians to destroy the tombs of the long line of Abbasid Caliphs, and then Hulegu summoned the captive Caliph to his camp outside the city. According to the Armenian chronicler Grigor of Akanc, Hulegu locked up the Caliph for three days without food or water, then brought him out and heaped up his gold and treasure before him. Pointing to the massive piles of wealth looted from the city, Hulegu reportedly ordered the Caliph to eat the gold, and when he could not scolded him for so greedily accumulating wealth instead of building an army to defend himself. He then sentenced the Caliph and his male heirs to death, but as a final gesture of respect for the high status of the condemned, he allowed them the honor of being executed in the Mongol way—without bloodshed. According to the differing but similar accounts, they were either wrapped in carpets or else sewn into sacks and kicked to death by the Mongol warriors or trampled by their horses.