While Asad ibn `Abdullah el-Kasrī[210] held the governorship of Khorāsān a certain nobleman of Balkh named Sāmān,[211] who had been driven out of his native town, came to Asad in Merv and begged the governor to help him against his enemies. Asad warmly espoused his cause and succeeded in reinstating him in Balkh. Out of gratitude for this action, Sāmān, who had hitherto been a Zoroastrian,[212] embraced Islām and named his son Asad after his protector. This Asad had four sons, who rendered excellent services to Hārūn er-Rashīd in quelling the revolt of Rāfi` ibn Layth.[213] Ma´mūn, mindful of the obligations under which the sons of Asad had placed his father, ordered the then governor of Khorāsān, Ghassān ibn `Abād,[214] to give to each of them the government of a town. Thus in the year A.H. 202 (817)[215] Nūh, the eldest son, became Amīr of Samarkand; Ahmed, Amīr of Farghāna; Yahya, Amīr of Shāsh (Tashkent) and Oshrūsana; and Ilyās, lord of Herāt.[216] When, in A.H. 205, Ghassān was superseded by Tāhir, these grants to the family of Sāmān were confirmed, and continued in the same hands until the downfall of the Tāhirides and the rise of the Sāmānides to the supreme power in the East. In A.H. 213 (828) Talha died and was succeeded by his son `Alī, who, however, perished shortly afterwards in a conflict with the Khārijites near Nīshāpūr. Ma´mūn thereupon sent Talha’s brother `Abdullah to Khorāsān to assume the reins of government, which he held until his death in A.H. 230 (844), at the age of forty-eight, after seventeen years of most successful administration. But although the Caliph’s name was scrupulously mentioned in Friday prayers, Khorāsān was now to all intents and purposes independent of Baghdād. The falling away of this essentially Persian province was but the first step towards the final separation of the Arabs and the Persians which was shortly to follow, after two hundred years of involuntary and unnatural association. The Tāhirides continued to rule Khorāsān and the East during a period of fifty-six years, when their last representative, Mohammad,[217] in A.H. 259 (872), was overthrown by the Saffāride Ya`kūb ibn Layth, of whom we must now speak. CHAPTER XIV THE SAFFĀRIDES AND THE RISE OF THE SĀMĀNIDES