Even in Christian times the practice continued; as women were sometimes forbidden to sing in Church, their place was taken by castrati. The practice remained popular until the 18th century and was known into the 19th century, the last famous Italian castrato did not die until early in the 20th century.
...snip...(Often guarded the women and children)
“The English form of the Greek word which means bed-keeper . In the strict and proper sense they were the persons who had charge of the bed-chambers in palaces and larger houses. But as the jealous and dissolute temperament of the East required this charge to be in the hands of persons who had been deprived of their virility, the word eunuch came naturally to denote persons in that condition. But as some of these rose to be confidential advisers of their royal master or mistresses, the word was occasionally employed to denote persons in such a position, without indicating anything of their proper manhood.” -Abbott.
I read someone who said that MJ modeled himself after a famous Castrati . I don’t remember the name. Might have started with an F