Trisong Detsen: the Tibetan Empire at its height and the founding of Samye

Trisong Detsen, born in 742, came to the throne as a boy: his father Me Agtsom was killed in a palace plot in 755, and the son was enthroned the following year. The An Lushan rebellion drew the Tang armies away from the west, and Tibet pressed into their frontier lands; in late 763 a Tibetan army occupied Chang’an for about two weeks (fifteen days according to the Old Book of Tang) and set up a puppet emperor. A treaty of 783 fixed the border, but fighting soon resumed, while in the south Nanzhao remained under Tibetan overlordship until 794. In the north the Tibetans defeated the Uyghurs and the Tang at Beiting in 790, and in the west they fought the Abbasids: the Old Book of Tang says that in the Zhenyuan years (785–805) more than half of the Tibetan army was engaged in the west against the Arabs.

At home the young king first had to contend with ministers hostile to Buddhism, who in the late 750s expelled the Chinese and Nepali monks and desecrated the temples. Trisong Detsen sent missions to China for Buddhist teachings, and once the hostile ministers had been removed he invited Śāntarakṣita, a scholar of Nalanda. By Tibetan tradition, storms and misfortunes, blamed on angry local gods, hampered his preaching, and on his advice the king called in the tantric master Padmasambhava, who subdued the spirits. Samye was laid out on the plan of a mandala; according to the Testament of Ba, it was founded in a hare year and consecrated in a sheep year — either 763 and 767 or 775 and 779. About 779 the first Tibetan monks were ordained there; a pillar in front of Samye records the oath of the king, his ministers and nobles to preserve the temples and their endowments, and translators began the great work of rendering the Buddhist scriptures from Sanskrit into Tibetan.

In the early 790s (792–794 by the usual dating) the king presided at Samye over a debate between the Chinese Chan master Moheyan, who taught sudden enlightenment, and Śāntarakṣita’s disciple Kamalaśīla, who defended the gradual path. Tibetan accounts say that Kamalaśīla won and the king forbade the Chinese teaching; Chinese accounts claim victory for Moheyan. Later tradition honoured Trisong Detsen as the second of Tibet’s three Dharma kings. His reign ended in 797, when he either abdicated in favour of his son Muné Tsenpo or died — the sources differ.