The Muslim invasion of the Indian subcontinent was the first great iconoclastic invasion into the Indian subcontinent. According to William Johnston, hundreds of Buddhist monasteries and shrines were destroyed, Buddhist texts were burnt by the Muslim armies, monks and nuns killed during the 12th and 13th centuries in the Indo-Gangetic Plain region. The Buddhist university of Nalanda was mistaken for a fort because of the walled campus. The Buddhist monks who had been slaughtered were mistaken for Brahmins according to Minhaj-i-Siraj. The walled town, the Odantapuri monastery, was also conquered by his forces. Sumpa basing his account on that of Śākyaśrībhadra who was at Magadha in 1200, states that the Buddhist university complexes of Odantapuri and Vikramshila were also destroyed and the monks massacred. Muslim forces attacked the north-western regions of the Indian subcontinent many times. Many places were destroyed and renamed. For example, Odantapuri's monasteries were destroyed in 1197 by Muhammad bin Bakhtiyar Khilji and the town was renamed. Likewise, Vikramashila was destroyed by the forces of Muhammad bin Bakhtiyar Khilji around 1200. The sacred Mahabodhi Temple was almost completely destroyed by the Muslim invaders. Many Buddhist monks fled to Nepal, Tibet, and South India to avoid the consequences of war. Tibetan pilgrim Chöjepal (1179-1264), who arrived in India in 1234, had to flee advancing Muslim troops multiple times, as they were sacking Buddhist sites.