The Muslim conquests of Afghanistan began during the Muslim conquest of Persia as the Arab Muslims migrated eastwards to Khorasan, Sistan and Transoxiana. Fifteen years after the Battle of Nahāvand in 642 AD, they controlled all Sasanian domains except in Afghanistan. Fuller Islamization was not achieved until the period between 10th and 12th centuries under Ghaznavid and Ghurid dynasty's rule who patronized Muslim religious institutions. Khorasan and Sistan, where Zoroastrianism was well-established, were conquered. The Arabs had begun to move towards the lands east of Persia and in 652 AD they captured the city of Herat, establishing an Arab governor there. The Muslim frontier in modern Afghanistan had become stabilized after the first century of Hijri calendar as the relative importance of the Afghan areas diminished. From historical evidence, it appears Tokharistan (Bactria) was the only area heavily conquered by Arabs where Buddhism flourished. Balkh's final conquest was undertaken by Qutayba ibn Muslim in 705. Hui'Chao, who visited around 726, mentions that the Arabs ruled it and all the inhabitants were Buddhists. The eastern regions of Afghanistan were at times considered politically as parts of India. Buddhism and Hinduism held sway over the region until the Muslim conquest. Kabul and Zabulistan which housed Buddhism and other Indian religions, offered stiff resistance to the early Muslim advance. Nevertheless, the Arab Umayyads regularly claimed nominal overlordship over the Zunbils and Kabul Shahis, and in 711 Qutayba ibn Muslim managed to force them to pay tribute. They would also be conquered by the Saffarids and Ghaznavids. The Caliph Al-Ma'mun (r. 813–833 AD) was paid double the tribute by the Rutbil. His were the last Arab expeditions on Kabul and Zabul. The king of Kabul was captured by him and converted to Islam. The last Zunbil was killed by Ya'qub bin al-Layth along with his former overlord Salih b. al-Nadr in 865. Meanwhile, the Hindu Shahi of Kabul were defeated under Mahmud of Ghazni. Indian soldiers were a part of the Ghaznavid army, Baihaki mentioned Hindu officers employed by Ma'sud. The 14th-century Muslim scholar Ibn Battuta described the Hindu Kush as meaning "slayer of Indians", because large numbers of slaves brought from India died from its treacherous weather. The geographer Ya'qubi states that the rulers of Bamiyan, called the Sher, converted in the late 8th century. Ya'qub is recorded as having plundered its pagan idols in 870 while a much later historian Shabankara'i claims