In the year A.H. 141 (758) a strange sect of Persian origin styled Rāvandīs caused no little trouble to the Caliph, and even placed him in imminent personal danger.[193] The old chronicles have little to tell us of Khorāsān between the years A.H. 141 and 150, although during this period they have many grave events to record in other parts of the Caliph’s dominion,--such as the rising of Mohammad and Ibrāhīm, descendants of the martyred Hasan (A.H. 145), and the foundation of Baghdād, A.H. 145 (762). We also hear of frequent engagements in Armenia between the Caliph’s troops on the one hand and the Khazars and Turks on the other. These matters, however, do not directly concern our narrative.[194] We propose, therefore, to chronicle the years A.H. 150 to 180 briefly, recording only such facts as are connected with the history of Central Asia proper, and mentioning the names of those who held the governorship of Khorāsān during this period.[195] [Illustration: RELIGIOUS MENDICANT--BOKHĀRĀ] In A.H. 150 (767) a serious rising took place in Khorāsān, under the leadership of a Persian named Ustādsīs,[196] who, placing himself at the head of 300,000 men of Herāt, Bādghīs, Sistān, and other provinces, put to flight a large force of Khorāsānīs and men of Merv er-Rūd. On hearing of this, El-Mansūr immediately sent Khāzim ibn Khuzayma, who had been so successful in quelling the revolt in Mesopotamia, to help El-Mahdi, the governor of Khorāsān,[197] to meet this new danger. El-Mahdi gave over the supreme command of his troops to Khāzim, who led a force of 20,000 men to meet the rebel Ustādsīs. On approaching the enemy, Khāzim threw up a zariba and prepared for battle, whereupon Ustādsīs advanced to the attack. But while a portion of his army was forcing the entrenchments Khazim created a diversion by causing a body of his men to sally forth from an opening on the opposite side. This party fell on the rear of the rebel army and put them completely to rout, killing 70,000 and taking 14,000 prisoners. Khazim fled to the hills, but was at length obliged to surrender. A.H. 151 (768). El-Mahdi returned to Baghdād, and took up his residence in the new town of Rusāfa, which had been built for the Khorāsānīs, who were unable to dwell in peace with the haughty Arabs of the capital. A.H. 152 (769). Humayd ibn Kahtaba was appointed governor of Khorāsān, and proclaimed a Holy War against Kābul. A.H. 158 (774). El-Mansūr died, and was succeeded by his son El-Mahdi. A.H. 159 (775). Humayd was succeeded in the governorship of Khorāsān by Abu `Aun. A rising took place in Khorāsān in connection with the appointment of the heir-presumptive (_vali-`ahd_). A.H. 160 (776). Another rising occurred in Khorāsān under the leadership of Yūsuf ibn Ibrāhīm, called El-Barm, which was quelled by Yezīd ibn Mazyad. Yūsuf was sent captive to El-Mahdi, who, after subjecting him to the cruellest torture, crucified him.