Fortified manor houses (wubao 塢堡, wulei 塢壘, bilei 壁壘, leibi 壘壁, wubi 塢壁, baobi 堡壁, wu 塢, yingwu 營塢, wuhou 塢候) were private living spaces of magnates or landowners that were built with defensive means. Such fortified manors came up during the Han period 漢 (206 BCE-220 CE) in very remote regions like the Gansu Corridor. Examples of fortified manors can be found in tomb accessories from the Eastern Han period 東漢 (25-220 CE). Many of them had not only defensive walls, but also watchtowers, which could be used to give signals.
The high tide of fortified manors was during the Western Jin period 西晉 (265-316), when farms in north China were the object of raids by mounted groups of non-Chinese tribes like Xiongnu 匈奴 or Di 氐. In case of an attack, peasants and their families (often tenant farmers) could flee behind the walls.
Yet fortified manors had also military, social, political and economic functions. Most magnates from among the distinguished families (haoqiang 豪強) decided to protect their belongings by private armies (buqu 部曲) consisting of retainers and serfs. Apart from Chinese defending themselves against raids by "wild tribes", the many ethnicities living in north China during the 3rd and 4th centuries during the age of the Sixteen States 十六國 (300~430) made also use of fortifications to protect themselves against attacks from any other power, for instance, the Wuwan 烏丸 tribes in the northeast.
After the rebellion of the eight princes (ba wang zhi luan 八王之亂, Yongjia zhi luan 永嘉之亂), the central government of the Jin dynasty disintegrated, and the court fled to Jiankang 建康 (modern Nanjing 南京, Jiangsu), where the Eastern Jin dynasty 東晉 (317-420) was founded. North China was left in a status of political and social turmoil. Magnates took over the function of local government and also organized the daily needs of local society. They registered the population, organized the necessary labour, took care for defense, granaries, irrigation and other needs. When states were founded, like the Former Zhao empire 前趙 (304-329) by Liu Yuan 劉淵 (r. 304-309) or the Later Zhao empire 後趙 (319-350) of Shi Le 石勒 (r. 319-333), their governments used already existing structures like fortified manors in order to collect taxes, claim supplies for the army, or recruit peasants. The magnates took over the function of state officials.
Similar phenomena can be observed for regions belonging to the Eastern Jin empire. The weak central government made use of local powerholders to extend its reach without investing much in administrative infrastructure.
The troops protecting the fortified manors only served as soldiers in case of need. In peaceful times, they worked the fields. The uncertainties of the time prohibited trade and commerce, so that each manor was forced to rely on itself in economic terms and saw to it that all necessary products could be manufactured independently, and that the fields and orchards supplied all produce necessary for the community of the manor and its dependents. Rural self-subsistence thus replaced the exchange of produce between the countryside and the cities – all the more as most cities were devastated. Some fortified manors were so large that they were comparable to smaller districts with nearly a thousand households (Chen 2007: 85). Wubao structures became population centres in north China.
A less favourable aspect of the system of fortified manors was that peasants became more dependent on landowners, and many lost their status as free peasants to that of client-farmers (dianke 佃客), "hidden farmers" (yinke 蔭客) of even serfs.
The short-lived states ruling over north China accepted the infrastructure created by local magnates. When the Northern Wei dynasty 北魏 (386-534) unified north China, they continued this custom and accepted the owners of fortified manors as quasi-officials who took over government responsibilities. Only in the late 5th century century the system of local administration and defense by clan heads (zongzhu duhu 宗主督護) was replaced by a regular system of state officials who cooperated with village heads (see sanzhang zhi 三長制).