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In page Eunuch:

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Eunuchs existed in China from about 4,000 years ago, were imperial servants by 3,000 years ago, and were common as civil servants by the time of the Qin dynasty.[3][4] From those ancient times until the Sui dynasty, castration was both a traditional punishment (one of the Five Punishments) and a means of gaining employment in the imperial service. Certain eunuchs, such as the Ming dynasty official Zheng He,[citation needed] gained immense power that occasionally superseded that of even the Grand Secretaries. Self-castration was a common practice, although it was not always performed completely, which led to it being made illegal.[citation needed]