Khorasan. He moved south and then west, conquering but not wasting the cities in his path. In 1055 the caliph in Baghdad gave Tughril Beg robes, gifts, and the title King of the East. Under Tughril Beg's successor, Malik Shah (1072–1092), Iran enjoyed a cultural and scientific renaissance, largely attributed to his brilliant Iranian vizier, Nizam al Mulk. These leaders established the Isfahan Observatory where Omar Khayyám did much of his experimentation for a new calendar, and they built religious schools in all the major towns. They brought Abu Hamid Ghazali, one of the greatest Islamic theologians, and other eminent scholars to the Seljuk capital at Baghdad and encouraged and supported their work. A serious internal threat to the Seljuks during their reign came from the Hashshashin- Ismailis of the Nizari sect, with headquarters at Alamut between Rasht and Tehran. They controlled the immediate area for more than 150 years and sporadically sent out adherents to strengthen their rule by murdering important officials. Several of the various theories on the etymology of the word assassin derive from this group. Another notable Sunni dynasty were the Timurids. Timur was a Turco-Mongol leader from the Eurasian Steppe, who conquered and ruled in the tradition of Genghis Khan. Under the Timurid Empire, the Turco-Persian tradition which began during the Abbasid period would continue. Ulugh Beg, grandson of Timur, built an observatory of his own, and a grand madrassah at Samarkand. Shi'ism in Iran before the rule of the Safavids Although Shi'as have lived in Iran since the earliest days of Islam, the writers of the Four Books of Shi'a ahadith were Iranians of the pre-Safavid era and there was one Shi'a dynasty in part of Iran during the tenth and eleventh centuries, according to Mortaza Motahhari the majority of Iranian scholars and masses remained Sunni till the time of the Safavids. The domination of the Sunni creed during the first nine Islamic centuries characterizes the religious history of Iran during this period. There were however some exceptions to this general domination which emerged in the form of the Zaydīs of Tabaristan, the Buwayhid, the rule of Sultan Muhammad Khudabandah (r. Shawwal 703-Shawwal 716/1304-1316) and the Sarbedaran. Nevertheless, apart from this domination there existed, firstly, throughout these nine centuries, Shia inclinations among many Sunnis of this land and, secondly, original Imami Shiism as well as Zaydī Shiism had prevalence in some parts of Iran.