the disastrous 'Day of Thirst'. His troops, reinforced by men from the subject Hephthalite principality of Chaghaniyan, clashed with the Yemenis at Baruqan and prevailed over them. This led to resentment towards his person among the Yemenis, especially from those around Balkh; and during the governorship of the Yemeni Asad ibn Abdallah al-Qasri, along with other Mudari leaders, Nasr fell into disfavour and was mistreated. Nasr was one of the few Muslim leaders to distinguish himself in the disastrous Battle of the Defile in July 731. In 734 he was appointed as governor of Balkh, after arresting the previous governor. There he faced the rebellion of the local Khurasani troops under al-Harith ibn Surayj, who called for reforms in taxation and the ending of discrimination towards the native converts (). Ibn Surayj marched on Balkh and took the city with only 4,000 followers, even though Nasr commanded 10,000 men. It is unclear from the sources whether the town was seized from Nasr, or whether it was captured in his absence and then successfully held against him. In any case, Nasr and his army remained passive for the remainder of the revolt; they did not aid the provincial capital, Merv, when the rebels attacked it, and this stance encouraged several local tribes to join the uprising. Eventually however the rebels were defeated by Juday al-Kirmani, with Ibn Surayj fleeing across the Oxus to the Türgesh. Appointment as governor of Khurasan In July 738, at the age of 74, Nasr was appointed as governor of Khurasan. Despite his age, he was widely respected both for his military record, his knowledge of the affairs of Khurasan and his abilities as a statesman. Julius Wellhausen wrote of him that "His age did not affect the freshness of his mind, as is testified not only by his deeds, but also by the verses in which he gave expression to his feelings till the very end of his life". However, in the climate of the times, his nomination owed more to his appropriate tribal affiliation than his personal qualities. From the early days of the Muslim conquests, Arab armies were divided into regiments drawn from individual tribes or tribal confederations ( or ). Despite the fact that many of these groupings were recent creations, created for reasons of military efficiency rather than any common ancestry, they soon developed a strong and distinct identity. Eventually, and certainly