local cultures and languages to establish eastern Tibet, or Do Kham ('Do', the convergence of rivers and valleys; 'Kham', frontier). Kham was traditionally referred to as Chushi Gangdruk, i.e. 'The Four Rivers and Six Ranges' and 'The Four Great Valleys'. Responsible for introducing Buddhism to Tibet, King Songtsen Gampo (reign 629–649) built twelve 'border-taming' temples in Kham, and his 4th wife Wencheng Gongzhu is credited with commissioning Buddhist structures while traveling through Kham in 640–641, from her home in China to Central Tibet. During the Imperial era, both Nyingma school and Bon monasteries were located, especially in Nyarong Valley, among pastoral and agricultural-based polities ruled by local chieftains, polities which included merchant as well as Mongol and Chinese populations. Notable Tibetan Buddhist art from this era, dating from 804 or 816, includes carved stone statues of Buddha Vairocana. Following a power struggle in the mid-9th century, Tibet separated into independent kingdoms. 13th to 17th centuries Kham was not controlled by a single king and remained a patchwork of kingdoms, tribes, and chiefdoms whose bases of authority were constantly shifting. A dual system of secular and Buddhist polities continued. In 1270, the Sakya school's lama Tonstul, a student of Sakya Pandita, established a monastery in Kham while both Kagyu and Sakya monasteries were located in the northern plains, including Gonjo and Lingtsang, which accompanied the earlier Nyingma and Bon monasteries of Kham. In 1639, Güshri Khan, a supporter of the Dalai Lama, invaded with Mongolian troops and defeated the powerful King of Beri in Kham. In 1655, Ngawang Phuntsok, a student of the Dalai Lama, founded Gonsar Monastery, the first of the 13 Gelug monasteries in the Hor States, with the support of the kingdom of Degé. By 1677, many Gelug monasteries had been built when the 5th Dalai Lama finalized Kham's Sino-Tibetan border location between China and a Tibet then reunified in the Khoshut Khanate, resulting in Kham being ascribed to Tibet's authority. The major independent polities included the Chakla, Degé, the Lingtsang, Nangchen and the Lhatok. Other important polities included Chamdo, Batang, Mili, and the Hor States. 18th century In 1717, the Mongol Dzungar Khanate invaded Tibet and other Asian regions. The Qing Chinese army likewise invaded and defeated the Dzungars. This led to the redrawing of the Sino-Tibetan boundary of 1677, which had followed the edge of the Tibetan Plateau. The frontier line changed in either 1725 or