In the tenth century the Abbasid Caliphate lost control of most of its former provinces. Most of the governors were able to establish their own dynasties, and in the meantime the central government was unable to stop independence movements within the empire, though they retained their spiritual leadership over the Muslims since the new states acknowledged the Caliph as the head of the state and the successor of the prophet. In 1055, Tughril captured Baghdad from the Buyids under a commission from the Abbasid Caliphal-Qa'im. Although the Seljuqs respected the Caliphs, they did not let them rule.
The siege
Muhammad marched to Baghdad with an army of 30,000 men, while his ally Qutb ad-Din marched from Mosul to capture the Caliphate's provinces in central Iraq. On January 12, 1157, Muhammad reached the walls of western Baghdad. In response the Caliph gathered all his troops from Hillah and Wasit to defend the capital. In February, unable to defend western Baghdad, the caliph abandoned the western side and ordered all the bridges over the Tigris river, which separates the western side of Baghdad from its eastern side, to be destroyed. Muhammad crossed to the western side and easily captured it, and established his camp while at the same time the caliph fortified the walls of eastern Baghdad. Several catapults and ballistas were installed on the city's walls. The caliph also armed the natives of Baghdad by giving them armour and weapons, and incited them to fight the enemy of the caliphate, whom he called infidels since they waged war against the caliph, the successor of the prophet and the leader of the ummah. He also ordered his vizier Awn ad-Din ibn Hubayra to give five golden dinars to every wounded soldier. On March 4, Sultan Muhammad and his ally Zayn ad-Din, Qutb ad-Din's vizier, attacked eastern Baghdad and bombarded the city. The army of Baghdad repulsed the attack thanks to the courage of the natives of Baghdad and the naffatuns.
On March 29, the Seljuqs repaired one of the bridges and crossed to the eastern side of the city, where they skirmished with both the Caliph's army and the native militias of Baghdad. The naffatuns destroyed several catapults. The Seljuqs tried to breach the gate by a battering ram but it was destroyed by the catapults on the walls. The result of the battle remained indecisive for both sides. On June 29, Sultan Muhammad ordered his men to climb the walls. He had already made 400 ladders to climb the walls of Baghdad, but the assault was repulsed due to the heavy fire and casualties. In the meantime Nur ad-Din Zangi blamed his brother for attacking the caliph's realm, which destroyed the Zengid-Seljuq alliance. Zayn ad-Din lifted the siege and returned to Mosul. Muhammad also was forced to lift the siege after his men informed him that his brother Malik Shah has captured Hamadan. He eventually realized that the siege was useless, so he preferred to fight for his throne. Thus the Siege of Baghdad came to end on 13 July 1157.
