Trisong Detsen (Tibetan: ཁྲི་སྲོང་ལྡེ་བཙན, Wylie: khri srong lde btsan, Lhasa dialect: [ʈʂʰisoŋ tetsɛ̃]) was the son of Me Agtsom, the 38th emperor of Tibet. He ruled from AD 755 until 797 or 804. Trisong Detsen was the second of the Three Dharma Kings of Tibet, playing a pivotal role in the introduction of Buddhism to Tibet and the establishment of the Nyingma or "Ancient" school of Tibetan Buddhism.
The empire Trisong Detsen inherited had declined somewhat from its greatest extent under the first Dharma King, Songtsen Gampo. Disintegration continued when, in 694, Tibet lost control of several cities in Turkestan and, in 703, Nepal broke into rebellion. Meanwhile, Arab forces vied for influence along the western border lands of the Tibetan empire.
Trisong Detsen is very important to the history of Tibetan Buddhism as one of the three 'Dharma Kings' (Tibetan:chosgyal) who established Buddhism in Tibet. The Three Dharma Kings were Songtsen Gampo, Trisong Detsen, and Ralpacan.
The Skar-cung pillar erected by Sadnalegs (ruled c. 800-815) says that during the reign of Trisong Detsen, "shrines of the Three Jewels were established by building temples at the centre and on the borders, Bsam-yas in Brag-mar and so on". The first edict of Trisong Detsen already mentions a community of monks at Bsam-yas (Samye).
Trisong became emperor in 755 and, in post-imperial sources, is claimed to have invited Padmasambhava, Śāntarakṣita, Vimalamitra, and various other Indian teachers to come to Tibet to spread the latest understanding of the teaching. The two pandits began by establishing Samye as the first vihara in Tibet. Several Tibetans were eventually initiated as monks and a vast translation project was undertaken translating the Buddhist scriptures from Sanskrit into Classical Tibetan.
The first documented dissemination of Chan Buddhism to Tibet, chronicled in what has become known as the Statements of the Sba Family, occurred in about 761 when Trisong Detsen sent a party to the Yizhou region to receive the teachings of Kim Hwasang, a Korean Chan master, who they encountered in Sichuan. The party received teachings and three Chinese texts from Kim, who died soon after.
Trisong Detsen patronised a second party to China in 763. This second expedition was headed by a high minister, Sba Gsalsnan. There is scholarly dissent about whom Gsalsnan encountered in Yizhou. Early scholarship considered Kim, but this had been revised to Baotang Wuzhu (714-774), head and founder of Baotang Monastery in Chengdu. Both Kim and Baotang Wuzhu were of the same school of Chan, the East Mountain Teaching.
Trisong Detsen, hosted a famous two-year debate from 792-794, known in Western scholarship as the "Council of Lhasa" (although it took place at Samye at quite a distance from Lhasa) outside the capital. He sponsored a Dharma debate between the Chan Buddhist Moheyan, who represented the third documented wave of Chan dissemination in Tibet, and the scholar Kamalaśīla, a student of Śāntarakṣita. Effectively the debate was between the Chinese and Indian Buddhist traditions as they were represented in Tibet.
Sources differ about both the nature of the debate as well as the victor. Stein (1972: p. 66-67) holds that Kamalaśīla disseminated a "gradualist approach" to enlightenment, consisting of purificatory sādhanā such as cultivating the pāramitās. Kamalashila's role was to ordain Tibetans as Buddhist monks and propagate Buddhist philosophy as it had flourished in India. Stein (1972: p. 66-67) holds that Kamalaśīla was victorious in the debate and that Trisong Detsän sided with Kamalaśīla.
The role of Padmasambhava on the other hand was to establish the teaching of Buddhist Tantra in Tibet. During the reign of Trisong Detsän the combined efforts of Padmasambhava, Śāntarakṣita and Kamalaśīla established both the Indian Buddhist philosophical interpretation and Buddhist tantra in Tibet.
In 763 Trisong Detsen sent an army of 200,000 men to the border with Tang China, defeating the forces there and then continuing on to take Chang'an, the Tang Chinese capital, forcing Emperor Daizong of Tang to flee the capital. In 783 a peace treaty was negotiated between China and Tibet giving Tibet all lands in present-day Qinghai. The Tang Empire had declined greatly due to the An Lushan Rebellion which was finally quelled in 763.
Trisong Detsen next sought to expand westward, reaching the Amu Darya and threatening the Abbasid Caliph, Harun ar-Rashid. The Caliph was concerned enough to establish an alliance with the Chinese emperor. King Trisong Detsen would be preoccupied with Arab wars in the west, taking pressure off his Chinese opponents to the east and north, until his rule ended in 797.
Trisong Detsen retired to live at the palace at Zungkar and handed power to his second son, Muné Tsenpo, in 797. From this point there is much confusion in the various historical sources. It seems there was a struggle for the succession after the death of Trisong Detsen. It is not clear when Trisong Detsen died, or for how long Mune Tsenpo reigned. The Testament of Ba, a Tibetan historical text which may date back to the 9th century, claims that Muné Tsenpo insisted that his father's funeral be performed according to Buddhist rather than traditional rites.
Whatever the case, both the Old Book of Tang and the Tibetan sources agree that, since Mune Tsenpo had no heirs, power passed to his younger brother, Sadnalegs, who was on the throne by 804 CE.