The Treaty Pillar as it appeared in 1950. This pillar still exists outside the Jokhang Temple in Lhasa. Besides the Jokhang pillar, one was erected outside the Chinese emperor's palace gate in Ch'ang-an (now known as Xian, in Shanxi province.) and a third pillar was erected in 823 CE, at Gugu Meru on the border between the two countries (cf. "All to the east is the country of Great China; and all to the west is, without question, the country of Great Tibet" see below). The pillars at the Chinese imperial palace at at the border were destroyed when the the Tang dynasty was overthrown by invading Jurchens from present day Manchuria and the founding of the Song dynasty in 904 CE.
"The Lhasa Treaty pillar outside the Jokhang" 05 Dec. 2006. The Pitt Rivers Museum. Accessed 09 Nov. 2009
Frequently Communist propaganda will state that Tibet "has always" been a part of China. As this treaty makes plain, this is not so. The relations between the two countries appears to have been complex. On the one hand, the monument describes connections between China and Tibet as similar to those between uncle and nephew. The Tang dynasty of China and the Yarlung dynasty of Tibet were indeed related by marriage, yet the terms uncle and nephew are not used in relation to other groups with whom the Chinese had connections by marriage. On the other hand, the monument seems to describe the two countries as equals. The pillars were erected at the conclusion of a peace treaty marking the end of 200 years of intermittent warfare between the two kingdoms. The peace lasted for about 20 years. The pillar is inscribed in both Tibetan and Chinese.
translation: Richardson, Hugh, "The Sino-Tibetan Treaty Inscription of A.D. 821/823 at Lhasa," Journal of the Royal Asiatic Society 1978, no.2, pp.137-162.