after, however, their properties were confiscated—according to al-Tabari, that of al-Mu'tazz was valued at ten million dirhams—and imprisoned under the auspices of Bugha al-Saghir in one of the rooms of the Jawsaq Palace. Caliphate Rivalries between the Turkish leaders led to a split in 865, when al-Musta'in, Wasif and Bugha left Samarra for Baghdad, where they arrived on 5/6 February 865. There they were joined by many of their followers, and allied with the city's Tahirid governor, Muhammad ibn Abdallah ibn Tahir, who began fortifying the city. The bulk of the Turks, however, remained in Samarra. Their position threatened by this coalition, they released al-Mu'tazz and proclaimed him caliph. On 24 February, al-Mu'tazz placed his brother Abu Ahmad (the future al-Muwaffaq) in charge of the army, and sent him to lay siege to Baghdad. Abu Ahmad played a leading role in the siege, which created a close and lasting relationship with the Turkish military, that would later allow him to emerge as the virtual regent of the caliphate alongside his brother al-Mu'tamid (). The siege dragged on until December 865, when a combination of privations, lack of money to pay its supporters, and the price hikes caused by the siege eroded support for al-Musta'in's regime. As a result, Muhammad ibn Tahir opened negotiations with the besiegers, and a settlement was reached, which amounted to a mutual compromise over the sharing of the empire's proceeds: the Turks and other troops of Samarra received two thirds of annual state revenue, while the remainder would go to Ibn Tahir and his Baghdad forces. As part of the agreement, al-Musta'in would abdicate, in exchange for an annual pension of 30,000 dinars. Thus on 25 January 866, after the surrender of Baghdad, al-Mu'tazz became officially the sole, legitimate caliph. Although he was placed upon the throne by the Turks, al-Mu'tazz proved a capable ruler, and determined to restore the authority and independence of his office. He appointed as his vizier Ahmad ibn Isra'il, who had formerly served as his secretary during al-Mutawakkil's reign. Al-Mu'tazz moved quickly to sideline any potential rivals. Thus, despite his pledge of safety to al-Musta'in, in October/November 866 al-Mu'tazz had his predecessor assassinated at al-Katul in Samarra. In the same way he had his younger brother al-Mu'ayyad executed, even after forcing him to again renounce his rights to succession. Finally, Abu Ahmad, although initially welcomed with much honour by the Caliph