Castration was a common enough punishment in ancient times. Piotr Scholz explains that the punishment of cutting off the "ears" and "nose" of a criminal could actually be a euphemism for partial and full castration. Mutilation had also occurred among the gods, as in the case of Anu/Cain. It must have also been imposed on royal victims from time to time, although I can't think of a specific example off hand.
Scholz states (Eunuchs and Castrati, p 26), "In the Near East, especially at the Persian court, castrated boys were in great demand as articles of commerce. The practice of castrating kidnapped male children and selling them into slavery was a secure source of income for centuries in an area stretching from China to Gibraltar. Although the Chinese established a special facility for performing castrations - a virtual monopoly that 'turned out' literally thousands of court eunuchs - the sale of castrati remained a flourishing branch of the slave trade ... "
I'm not sure why eunuchs were so prevalent and prominent in the Persian period. However, the fact that the eunuch was considered essential at that time would have been motivation enough to designate certain royal persons as such, whether they literally were or not. A royal person that had been literally castrated as a punishment for rebellion or loser in a succession battle would not have continued as a faithful servant in the victorious king's court. Rather, a trusted member of the royal family like Megabyzus might be called a eunuch. It would of course served to keep that family member humble, but also honored them as one entirely trusted by the king.
For these reasons, Megabyzus was not likely castrated, either partially or fully. What's more, his natural (dynastic) line apparently did continue throughout the Persian Period. We'll be able to trace it in later posts.
© Charles N. Pope, US Library of Congress. All rights reserved.