jūn (軍) literally just means "army". Theoretically, these were military districts placed in strategic areas of high military importance, commonly the frontiers. In this sense, they would have been a bit like the marches of Europe, responsible for coordinating regional defenses. Early military prefectures typically inherited that designation from the Tang or Five Dynasties periods.
However, in practice, military prefectures were essentially identical to normal prefectures. The Song Dynasty aggressively pursued a policy of "strengthen the stems, weaken the branches". To maintain control, the Song court thus appointed civilian, central government officials for three year terms as prefecture governors. The same was true of military prefectures. For example, the famed calligrapher and painter Mi Fu was appointed to the Huaiyang Military Prefecture.
In terms of military, the Song Dynasty was extremely wary of strong regional forces. Soon after its foundation, it placed much of the empire's military forces directly under central government control. The remaining forces, known as
xiāng jūn (廂軍), became local prefecture forces with a career military commander, but under the control of the (typically) civilian prefecture governor. These were regular forces, however. There were also
xiāng bīng (鄉兵), which were more like seasonal conscripts raised in some regions - especially among the military prefectures of Shaanxi. Neither of these were effective fighting forces.
Song China had a three tier local government system. From top to bottom:
- Circuits -
- Prefectures -
zhōu (州) or equivalent
- Counties -
xiàn (縣) or equivalent
The circuits were essentially a supervisory organ, designed to monitor the prefectures without wielding much in the way of real authority over the latter. The four types of prefectures were substantially the same, except the more important prefectures were called
fǔ (府), the military focused prefectures were called
jūn (軍), and the
jiān (監) were typically counties with important resources or production, and often did not actually govern civilians.
The last were elevated to the rank of prefectures on account of being directly responsible to the central government, somewhat akin to the imperial immediacy of Europe. The normal prefectures were by far the most common type.
In addition to prefectures, both
jūn (軍), and the
jiān (監) were also designations for some counties. These fell under the administration and authority of a prefecture, rather than to the Imperial centre directly.