A number of monasteries grew up during the Pāla period in ancient Bengal and Magadha. According to Tibetan sources, five great Mahaviharas stood out: Vikramashila, the premier university of the era; Nalanda, past its prime but still illustrious, Somapura, Odantapura, and Jagaddala. The five monasteries formed a network; "all of them were under state supervision" and there existed "a system of co-ordination among them. It seems from the evidence that the different seats of Buddhist learning that functioned in eastern India under the Pāla were regarded together as forming a network, an interlinked group of institutions," and it was common for great scholars to move easily from position to position among them.Vikramashila was founded by Pāla king Dharmapala in the late 8th or early 9th century. It prospered for about four centuries before it was destroyed by Bakhtiyar Khilji along with the other major centres of Buddhism in India around 1193.Vikramashila is known to us mainly through Tibetan sources, especially the writings of Tāranātha, the Tibetan monk historian of the 16th–17th centuries.Vikramashila was one of the largest Buddhist universities, with more than one hundred teachers and about one thousand students. It produced eminent scholars who were often invited by foreign countries to spread Buddhist learning, culture and religion. The most distinguished and eminent among all was Atisha Dipankara, a founder of the Sarma traditions of Tibetan Buddhism. Subjects like philosophy, grammar, metaphysics, Indian logic etc. were taught here, but the most important branch of learning was Buddhist tantra.