ranks of the Turks, threatened the stability of the regime. At the beginning of 865, a quarrel among the Turkish officers broke out, and the general soldiery quickly became involved. When one of the officers was killed, the soldiers turned violent, and soon they were rioting throughout the streets of Samarra. Faced with this hostile situation, al-Musta'in and two of the senior Turkish officers, Wasif and Bugha al-Sharabi, decided to leave Samarra for Baghdad, where they were arrived in the first week of February 865. Upon their arrival, they were greeted by the city's powerful Tahirid governor, Muhammad b. 'Abdallah, in whose palace the caliph took up his residence. When the Turks in Samarra realized that al-Musta'in had departed from the city, they cut off traffic to Baghdad. A delegation of Turks then went to see the caliph; when they arrived, they asked for forgiveness for their actions and for the caliph to return with them to Samarra. Al-Musta'in, while promising the Turks that they would continue to be paid, refused to leave Baghdad, and he and Muhammad b. 'Abdallah mocked them for their perceived insolence. The humiliated Turks angrily returned to Samarra and told their compatriots what had happened; they then decided to depose al-Musta'in. The soldiers released al-Mu'tazz from his prison and acknowledged him as their caliph. Al-Mu'tazz agreed to the proposal and an oath of allegiance was drawn up; many of the officials in Samarra then swore allegiance to him. Beginning of hostilities With two members of the Abbasid dynasty now claiming to be caliph, war became inevitable. On al-Musta'in's side, Muhammad b. 'Abdallah quickly took command of the military effort. He ordered that all food shipments from Baghdad to Samarra be halted, and instructed allies in the Mosul region to do the same. Letters were sent by Muhammad to friendly commanders calling on them to mobilize their forces, and a recruitment drive was initiated in Baghdad. In preparation for a siege, the city was fortified, with the work being completed by February 22. The bridges and canals around al-Anbar were destroyed, flooding the area and hindering any possible enemy troop movements there. Muhammad also wrote to the tax officials throughout the empire, instructing them that their revenues were to be sent to Baghdad instead of Samarra. For his part, al-Mu'tazz wrote to Muhammad, urging him to declare allegiance to him. Soon after, al-Mu'tazz put his brother