During the Han Dynasty, most of the supervisors were recommended by local officials  In order to ensure that the imperial history exercised the power of impeachment without restraint, the Sui and Tang dynasties changed the system in which the official was selected and appointed by the official department since the Northern Wei Dynasty, but the selection of the official department in the Tang Dynasty was actually controlled by the prime minister  In the Song Dynasty, most of the supervisors at the central level were promoted by emperors, while the local supervisors implemented the official self-selection system, which was directly appointed by the central supervisors, and the supervisory power got rid of the control of the prime minister's power  In order to prevent nepotism, there will also be some restrictions on qualifications and avoidance  For example, in the Wei, Jin, Southern and Northern dynasties, great scholars were not allowed to serve as imperial magistrates, and in the Song Dynasty, relatives recommended by prime ministers as officials or prime ministers were not allowed to be imperial histories
In the Ming Dynasty, itinerant supervisors should avoid their places of origin, or had served as officials or lived in places
The difference between ancient supervisors and other official positions