The Tang–Tibet treaty of 821–822 and the treaty pillar in Lhasa

After the An Lushan rebellion Tibet had taken the western lands of the Tang, among them the Hexi Corridor, and it fought both the Tang and their Uyghur allies; earlier attempts at peace, such as the treaty of 783, had soon broken down. In 821, angered by a new Tang marriage alliance with the Uyghurs, the Tibetans attacked a Chinese frontier post, but in the autumn their envoys came to Chang’an to ask for a treaty. On 8 November 821, at an altar in the western suburb of the capital, the chief ministers Cui Zhi, Wang Bo and Du Yuanying and other dignitaries swore the oath with the Tibetan envoy Lun Naluo, and their names were written into the treaty.

The Tang envoy Liu Yuanding then travelled to Tibet with Lun Naluo. His road crossed former Tang lands, and at Longzhi a thousand old men, once Tang soldiers, bowed and wept before him, asked whether the court still remembered them and when its armies would come, and said that their sons and grandsons had not forgotten Tang dress. He reached the Tibetan court on the 24th day of the 4th month, and at the feast given on his arrival the performers, all Chinese, played Tang music. On the 6th day of the 5th month — the end of May 822 — the oath was sworn again, by the pillar’s account in a park east of Lhasa, by the Chinese account at the king’s summer camp on the north side of the Tsangpo, about a hundred li south of the city. A great monk who served the king as chief minister read it out and, unlike the others, did not smear his lips with the sacrificial blood, and the parties then swore once more by the Buddha. The treaty confirmed the border where each side then stood — the Tang were to supply envoys east of the Suirong stockade, Tibet west of Qingshui county — so that Hexi and Tibet’s other conquests remained Tibetan; it forbade raids and invasions and required people seized at the frontier to be questioned and sent home with clothes and food. “Tibetans shall be happy in Tibet and Chinese shall be happy in China,” the text declares.

The bilingual text was carved on a stone pillar in front of the Jokhang in Lhasa. According to its eastern face, the pillar was set up on the 14th day of the 2nd month of the third Changqing year — late March 823 — in the presence of the Tang envoy Du Zai, and a stele with the same text stood in Chang’an; Tibetan histories mention a third on the border. Only the Lhasa pillar survives. Its western face bears the treaty in Tibetan and Chinese, the northern and southern faces the names and titles of the Tibetan and Tang ministers who swore it — the Tibetan list is headed by a Buddhist monk — and the eastern face a Tibetan account of relations between the two courts since the marriages of the princesses Wencheng and Jincheng, which had made the Tang emperor and the Tibetan king “uncle and nephew”. The peace held for some two decades, until the collapse of both Tibetan and Uyghur power in the 840s.