Yarlung Dynasty
The diffusion of Buddhism among the peoples of the Tibetan Plateau, beginning in the 7th century AD, promoted many aspects of inter-regional social and political cohesion. most notably the acceptance of a standardized writing system designed to transmit the teachings of the Buddha. Today, Tibetans still revere King Songtsen Gampo of the Yarlung Dynasty, who ruled in this time over a Tibetan empire that stretched from the western edges of the Tibetan Plateau to the borders of Tang China along Gansu and Sichuan provinces in the east. Tibetís influence was so great, in fact, that in the year 763, the Tibetans, allied with the Uighur Turks, invaded the Tang Empire, captured the Chinese capital Chang-an, and replaced the Tang emperor with a candidate of their own choosing. The Tibetan empire in the era of the Yarlung kings and the Tang Dynasty, as shown in Map I, thus clearly extended beyond the physiographic limits of the Tibetan Plateau to include parts of China. (the area of color fade on other maps demarks the approximate eastern edge of Tibetan civilization and the Tibetan Plateau.)
During this period Tibet and China negotiated a series of treaties, the most famous of which ids the Treaty of 821-822, and which was inscribed on three stone pillars. One pillar was placed in the Chinese capital, Xiían (Chang-an), and another along the border at Gugumeru. The third was placed in Lhasa and still stands today. (A facsimile of this pillar may be found in the upper left-hand corner of this map.) This pillar treaty leads to agreed-upon borders between both sides, and was the seventh such treaty concluded between Tibet and Tang China. Though no specific maps relating to this treaty are known to exist that would help in demarcating the frontier from this time, an old Chinese book version of the treaty text notes that the territory of China was specified as lying to the east of two rivers, the Tao He, located south of Lanzhou, and the Ming Jiang, located south of Chengdu. Contemporary Tibetan assertions that Tibet comprises not only U-Tsang but also Amdo and Kham are heavily influenced by this definitive historical period when Tibet stood as a political and military equal with China.
The inscription of the treaty of 821-822 provides numerous examples of how the frontier between Tibet and China was understood and demarcated --mainly in terms of specific border posts. The closest reference to a de jure boundary provided by the treaty states: "both Tibet and China shall keep the country and frontiers of which they are now in possession. The whole region to the east of that being the country of Great China and the whole region to the west being assuredly the country of Great Tibet." (Richardson 1978). Other versions of the text of the treaty, such as that preserved in the Chinese dynastic record, the old Tang History (Jiu Tangshu), also refer to "strategic places and posts of defense (that) shall be carefully kept as before" (Pan 1992).
