south of the Hindu Kush until about 185 BC when they were overthrown. At the time of these developments, most of the area belonged to the kingdoms of Bactria and Sogdiana, including the Scythians, followed Buddhism until the arrival of Islam. After the Mauryan Empire, Buddhism also flourished under the Kushan Empire, when a tribe called the Yuezhi conquered Bactria and entered the region of modern day Afghanistan. Many monuments testify to the Buddhist culture in present-day Afghanistan. Additional historical detail can be researched under Pre Islamic Hindu and Buddhist heritage of Afghanistan and Hinduism in Afghanistan. Soon after the Sassanian Persian dynasty fell to the Muslims (in 651 AD), the Nava Vihara monastery in Balkh came under Muslim rule (in 663 AD), but the monastery continued to function for at least another century. In 715 AD, after an insurrection in Balkh was crushed by the Abbasid Caliphate, many Persian Buddhist monks fled east along the Silk Road to the Buddhist Kingdom of Khotan, which spoke a related Eastern Iranian language, and onward into China. Nava Vihara's hereditary administrators, the Persian Barmakids, converted from Buddhism to Islam after the monastery's conquest and became powerful viziers under the Abbasid caliphs of Baghdad. The last of the family's line of viziers, Ja'far ibn Yahya, is a protagonist in many tales from the Arabian Nights. In folktales and popular culture Ja'far has been associated with a knowledge of mysticism, sorcery, and traditions lying outside the realm of Islam. The Buddhist religion survived the Islamic conquest of Afghanistan by the Umayyads and rule by the Abbasid Caliphate. Buddhism in Afghanistan was effectively destroyed in the 13th century by Mongol armies during the Mongol conquests. Archaeological finds Bamiyan monastery library One of the early Buddhist schools, the Mahāsāṃghika-Lokottaravāda, were known to be prominent in the area of Bamiyan. The Chinese Buddhist monk Xuanzang visited a Lokottaravāda monastery in the 7th century CE, at Bamiyan, Afghanistan, and this monastery site has since been rediscovered by archaeologists. Birchbark and palm leaf manuscripts of texts in this monastery's collection, including Mahāyāna sūtras, have been discovered at the site, and these are now located in the Schøyen Collection. Some manuscripts are in the Gāndhārī language and Kharoṣṭhī script, while others are in Sanskrit and written in forms of the Gupta script. Manuscripts and fragments that have survived from this monastery's collection include the following source texts: Pratimokṣa Vibhaṅga of