Administrative divisions of the Tang dynasty

The Tang dynasty administered territory using a hierarchical system of three descending divisions: circuit dào (道), prefecture zhōu (州), and county xiàn (縣). Prefectures have been called jùn 郡 as well as zhōu 州 interchangeably throughout history, leading to cases of confusion, but in reality their political status were the same. The prefectures were furthered classified as either Upper Prefectures (shàngzhōu 上州), Middle Prefectures (zhōngzhōu 中州), or Lower Prectures (xiàzhōu 下州) depending on population. An Upper Prefecture consisted of 40, 000 households and above, a Middle Precture 20, 000 households and above, and a Lower Prefecture anything below 20, 000 households. Some prefectures were further categorized as bulwark prefectures, grand prefectures, renowned prefectures, or key prefectures for strategic purposes. A superior prefecture was called a fu (府).

The scope and limits of each circuit's jurisdiction and authority differed greatly in practice, and often individual circuit inspectors' powers and autonomy grew to a point that the administrative system became popularly known as the "Three Divisions of Falsehood" (虛三級). As Tang territories expanded and contracted, edging closer to the period of Five Dynasties and Ten Kingdoms, administrative records of these divisions became poorer in quality, sometimes either missing or altogether nonexistent. Although the Tang administration ended with its fall, the circuit boundaries they set up survived to influence the Song Dynasty under a different name: lù (路).

Emperor Taizong (r. 626−649) set up 10 "circuits" (道, dào) in 627 as areas for imperial commissioners to monitor the operation of prefectures, rather than as a direct level of administration. In the early Tang these geopolitical entities were not based on the realities of governance but rather ease of use when communicating which areas were to be monitored by the imperial commissioners. Prefects answered directly to the central government until the mid Tang Dynasty when circuits took on new governmental responsibilities. In 639, there were 10 circuits, 43 commanderies (都督府, dūdū fǔ), and 358 prefectures (州 and later 府, fǔ). In 733, Emperor Xuanzong expanded the number of circuits to 15 by establishing separate circuits for the areas around Chang'an and Luoyang, and by splitting the large Shannan and Jiangnan circuits into 2 and 3 new circuits respectively. He also established a system of permanent inspecting commissioners, though without executive powers. In the year 740 CE, the administrative establishments of the Tang Dynasty reached 15 circuits, 328 prefectures, and 1573 counties. Under the reforms of Emperors Zhongzong, Ruizong, and Xuanzong, these circuits became permanent administrative divisions. Circuits were assigned a number of permanent imperial commissioners of varying purposes and titles starting around the year 706 CE.

...
Wikipedia