Map Introduction

Historical Evolution of the Western Longyou Circuit in the Tang Dynasty (7th–9th Centuries)

I. Administrative Establishment and Territorial Scope

The Longyou Circuit was one of the ten circuits established in the first year of the Zhenguan era (627 AD) of the Tang Dynasty, named for its location west of the Long Mountains (Liupan Mountains). Its western territory stretched from Qin Prefecture (modern Tianshui) in the east to beyond the Aral Sea in the west, bordering the Tibetan Empire to the south and the Mongolian Plateau to the north. It encompassed western modern Gansu, eastern Qinghai, and eastern Xinjiang. Its core areas included Liang Prefecture (Wuwei), Gan Prefecture (Zhangye), Su Prefecture (Jiuquan), Sha Prefecture (Dunhuang), and the two major Protectorates – Anxi and Beiting. This region was the crucial corridor for Tang control over the Silk Road.

II. Military Defense and Strategic Evolution

• Early Tang Layout: Initially focused on defending against the Tuyuhun and Dangxiang Qiang peoples, with Song Prefecture (modern Songpan) serving as an outpost. Later, with the rise of the Tibetan Empire, the defensive focus shifted west to Shan Prefecture (Ledu, Qinghai) and Liang Prefecture.
• Jiedushi System: During the Kaiyuan era, the Hexi and Longyou Military Commissioner offices were established, headquartered in Liang Prefecture and Shan Prefecture respectively, to coordinate military and administrative affairs. The Hexi Military Commissioner governed prefectures like Liang, Gan, and Su, while the Longyou Military Commissioner was responsible for prefectures like Shan, Tao, and Die.
• Collapse after the An Lushan Rebellion: During the An Lushan Rebellion (755–763 AD), elite troops from Longyou were transferred east to suppress the rebellion. The Tibetan Empire seized the opportunity to capture Qin, Wei, Tao, and other prefectures. Liang Prefecture fell in 763 AD, leading to the loss of most of the western Longyou region.

III. Economy and Ethnic Integration

• Agricultural and Pastoral Development: The western Longyou region practiced mixed farming and pastoralism. Military agricultural colonies in Liang and Gan prefectures were highly successful. Guo Yuanzhen's implementation of irrigation projects in Gan Prefecture resulted in bountiful harvests described as yielding "dozens of hu of grain for one bolt of silk."
• Role as an Ethnic Corridor: As a vital hub on the Silk Road, it was inhabited by Tuyuhun, Dangxiang, Uighur, and other groups. In the 9th century, the Hexi Uighurs (Ganzhou Uighurs) established a regime and maintained close relations with the Tang court.

IV. Cultural Influence and Legacy

• Spread of Buddhism: The construction of the Mogao Caves in Sha Prefecture and the Yulin Caves in Gua Prefecture reflected Longyou's role as a pivotal hub for the eastward transmission of Buddhism.
• Administrative Legacy: Its administrative structure laid the foundation for the later administrative divisions of Gansu and Qinghai. The territorial concept of "bordering Qin Prefecture in the east and extending beyond the Flowing Sands (deserts) in the west" had a profound lasting influence.

Conclusion

The rise and fall of the western Longyou Circuit were inextricably linked to the fortunes of the Tang Dynasty: it served as a crucial frontier stronghold in the early Tang but gradually declined during the mid and late Tang due to Tibetan invasions. This process reflects the successes and failures of Tang frontier governance and shaped the historical pattern of multi-ethnic integration in the northwest.