The new caliph al-Ma'mun remained for several years in his eastern headquarters of Marv. Although Tahir was one of the architects of his triumph, he ordered Tahir to relinquish control of western Persia, Iraq and the Arabian peninsula to al-Hasan, brother of his principal adviser, the Persian al-Fadl b. Sahl, called Dhu'l-Riyasatain ("the man charged with the two functions, al-tadbir wa al-harb",, i.e. civil and military power). Instead, he was appointed governor of al-Jazira and Syria, with the specific charge of combating a local Arab chief, Nasr b. Shabath al-'Uqaili, who had raised a revolt of pro-Aminid elements. In the event, he made no real headway, and Nasr b. Shabath continued to cause trouble for over ten years, until his centre of power at Kaisum, north of Aleppo, was captured. Tahir's base during these years was at Raqqa on the Euphrates, but he also acquired further offices in Iraq, becoming sahib al-shurta, the officer responsible for public order and police services, in Baghdad, and taking over responsibility for collection of the revenues of the Sawad of Iraq, the fertile and prosperous agricultural region of central Iraq. Whilst the Tahirids have come to be primarily known for their rule in Khurasan, these administrative charges in Baghdad were hardly of less importance for the maintenance of the family's power; indeed, various Tahirids held on to them till the early years of the 10th century, long after Khurasan had been relinquished to the Saffarids. They were undoubtedly very lucrative. According to Ya'qubi, the khardj or landtax of Khurasan under the Tahirids amounted to forty million dirhams, but as well as this, their interests in Iraq brought them an extra thirteen million dirhams, plus other revenue in kind. Within the city of Baghdad, the Tahirids were rich property-holders. The Harim of Tahir b. al-Husain, one of the most opulent buildings in the western side of Baghdad, was the residence of the Tahirid governors of Baghdad, and later, of the caliphs themselves; as early as 'Abd-Allah b. Tahir's time, it acquired quasi-regal status, with consequent rights of sanctuary (hence the name harim "inviolable place, sanctuary"). By means of these offices, the Tahirids were able to exert influence at the centre of the caliphate, and since their seat was in Baghdad, they were less affected by the violence of the Turkish guards who dominated and often terrorized the caliphs in Samarra. Thus Tahirid pressure in Baghdad compelled the Caliph al-Mu'tamid to take a firm line, if only temporarily, against Ya'qub b. al-Laith when in 259/873 he captured Nishapur from Muhammad b. Tahir.
Tahirid Dynasty, Their Origin and Political Status under Abbasids
