Map Introduction

I. Administrative Establishment and Military Defense System

The eastern part of the Longyou Circuit (modern eastern Gansu and southern Ningxia) was formally established as a circuit in the 1st year of the Zhenguan era (627 AD). It governed prefectures such as Qin, Wei, and Yuan, forming an administrative and military framework centered on Liang Prefecture (Wuwei). Militarily, a three-tiered "Military Governor – Garrison Town – Beacon Tower" system was implemented. In the 2nd year of the Jingyun era (711 AD), the Hexi Military Governor was established, headquartered in Liang Prefecture, commanding 73,000 troops and 19,000 horses. During the Kaiyuan era, the Longyou Military Governor was added, stationed in Shan Prefecture (Ledu, Qinghai), creating a coordinated north-south defensive posture. Notably, Yuan Prefecture (Guyuan) served as the core of the Pasturage Lands, with horse-grazing areas stretching 600 li east-west and 400 li north-south, expanding further into the Hexi Corridor during the Tianbao era.

II. Ethnic Conflicts and Frontier Rivalries

This region long faced dual pressure from the Turks and the Tibetan Empire: during the Wude era, the Turks invaded Gan Prefecture via the Zhangye River valley four times (620-624 AD). After the Tibetan Empire annexed the Tuyuhun in the 3rd year of the Longshuo era (663 AD), the eastern Longyou Circuit was directly exposed to the Tibetan threat. The Tang Dynasty employed a strategy of "using barbarians to control barbarians," such as enfeoffing the Tuyuhun leader Nuohebo as Khan in the 9th year of Zhenguan (635 AD). However, after the 1st year of the Xiantian era (712 AD), the Tibetans repeatedly contested the He-Long region (the corridor between the Yellow River and the Long Mountains), causing strategic strongholds like Liang Prefecture and Gan Prefecture to change hands multiple times.

III. Economic Development and Transportation Network

Leveraging river systems like the Shiyang River and Heihe River, a trinity economic model of "Military Farms – Pasturage Lands – Border Markets" was formed. Guo Yuanzhen's military farms in Gan Prefecture achieved harvests so abundant that "one bolt of silk could be exchanged for dozens of hu of grain." Meanwhile, the border market in Liang Prefecture became a trade hub between the Central Plains and the Western Regions, with annual trade volume exceeding one million strings of cash during the Tianbao era. For transportation, the Zhangye River Valley (Ruoshui River) and the Macheng River Valley (Shiyang River) constituted two north-south military corridors, with the Zhangye River Valley serving as the primary route for Turkic incursions.

IV. Historical Impact and Final Fall

After the An Lushan Rebellion (755 AD), garrison troops from Longyou were transferred eastward. The Tibetan Empire seized the opportunity to capture the Eleven Prefectures of Hexi, gaining complete control over the eastern Longyou Circuit by the 1st year of the Guangde era (763 AD). Although Qin and Wu Prefectures were briefly recovered during the Dazhong era (847-860 AD), the Tang ultimately failed to restore its former territory. The evolution of this region confirms its strategic value encapsulated by the saying, "Whoever controls Longyou commands the Western Regions." Its military-administrative system profoundly influenced the later governance of the Hexi Corridor.