Trisong Detsän or Trisong Detsen ཁྲི་སྲོང་ལྡེ་བཙན (Tibetan Wylie: khri srong lde btsan [ʈʂʰisoŋ tetsɛ̃]; PRC: Chisong Dêzain; THDL: Trisong Detsen; other transcriptions: Trisong Detsan, Thrisong Detsän; traditional Chinese: 赤松德贊; simplified Chinese: 赤松德赞; pinyin: Chìsōng Dézàn; Thi-srong-detsan), was the son of Me Agtsom and one of the emperors of Tibet and ruled from 755 until 797 or 804 CE. 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.
Trisong had five wives, all of whom came from Tibetan noble families. According to the later hagiographic tradition of Padmasambhava, Yeshe Tsogyal, the Princess of Karchen was a wife of the emperor and also one of Padmasambhava's consorts. She is said to have recorded Padmasambhava's teachings and became known for her own Buddhist realizations. Another wife, Tse Pongza, the principal wife of Trisong Detsen, and the mother of the heir apparent, became known for being the counterpole of Padmasambhava and Yeshe Tsogyal, fighting for the Bön religion and against Buddhism. One of Trisong Detsen's children was Princess Pema Sal, who was entrusted by Padmasambhava with an important terma.
The empire Trisong Detsen inherited had declined somewhat from its greatest extent under the first Dharma King, Songtsen Gampo. Disintegration continued during Trisong Detsen's reign 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 and his support for Buddhism 
Part of a seriesTibetan Buddhism
|Practices and attainment|
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 Songtsän 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).
Indian traditions 
Trisong became emperor in 755 and, in post-imperial sources, is claimed to have invited Padmasambhava, Shantarakshita, 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 Monastery as the first Buddhist monastery in Tibet. Several Tibetans were eventually initiated as monks and a vast translation project was undertaken translating the Buddhist scriptures from Sanskrit into Tibetan.
Chinese traditions 
Ray (2005) holds that the first documented dissemination of Ch'an to Tibet, chronicled in what has become known as the Statements of the Sba Family, occurred in c761CE when Trisong Detsen sent a party to the I-chou region to receive teachings of Reverend Kim Kim Hwasang, a Korean Ch'an master, whom they encountered in Szechwan. The party received teachings and three Chinese texts from Reverend Kim. Reverend Kim died soon after.
Ray (2005) holds that Trisong Detsen patronised a second party to China in 763CE. This second expedition was headed by Gsal-snan, of the Sba family. There is scholarly dissent about whom Gsal-snan encountered in I-chou. Early scholarship considered Reverend Kim, but this had been revised to Pao-t'ang Wu-chu (Chinese: 無住; 714-774CE), head and founder of Pao-t'ang Monastery (Chinese: 保唐寺) at Chengtu. Both Reverend Kim and Pao-t'ang Wu-chu were of the same Ch'an variety, the "East Mountain Teaching" incorrectly known in Western scholarship with the pejorative nomenclature, "Northern School".
Trisong Detsen, hosted a famous two-year debate from 792-794 CE, 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 Chinese Ch'an Meditation Master Mo-ho-yen (who represented the third documented wave of Ch'an dissemination in Tibet) and the scholar Kamalashila, a student of Shantarakshita. 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 Kamalashila disseminated a "gradualist approach" to enlightenment, consisting of purificatory sadhana such as cultivating the Six Perfections. 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 Kamalashila was victorious in the debate and that Trisong Detsen sided with Kamalashila.
Stupa construction 
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, Shantarakshita and Kamalashila established both the Indian Buddhist philosophical interpretation and Buddhist tantra in Tibet.
Political and military activities 
In 763 Trisong Detsän 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 Chinese capital, forcing the Tang Emperor to flee the capital. In 783 a peace treaty was negotiated between China and Tibet giving Tibet all lands in the Kokonor region. At that time, the Tang Empire had started its decline due to the Anshi Rebellion.
Trisong Detsän next sought to expand westward, reaching the Oxus River and threatening the Arab Caliph, Harun al-Rashid. The Caliph was concerned enough to establish an alliance with the Chinese emperor,  Through the remainder of his reign the King 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.
Retirement, death and succession 
Trisong Detsen retired to live 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 dBa' bzhed, 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 the Bon rites.
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- Princess Pema Sal - RangjungYesheWiki
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- Stein, R. A. (1972) Tibetan Civilization, p. 131. Stanford University Press. ISBN 0-8047-0806-1 (cloth); ISBN 0-8047-0901-7 (pbk)
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r. 755-797 or 804