First let me point out that it is incorrect to use the term “castrato” for a man who has been simply gelded; the proper term for those is, indeed, eunuch. A castrato was one who, between the ages of eight and puberty, had undergone a highly specialized procedure which left him incapable of insemination, although most of them seem to have been fully capable of initiating intercourse (however, at least one site I read claimed that the <ahem> size of the equipment suffered). Indeed, it appears to me that retaining the capacity to produce at least some male hormones was vital, as without them, the (usually) enhanced vocal range, and especially the greatly enhanced volume and voice support would never have been realized.[sup]1[/sup] Castrati were made in order to have males who could sing female ranges with the volume and resonance of men, and were in demand with the various Crusader knightly orders for the singing of Masses, as well as with the creators of secular vocal music. If you check into some of the links, you’ll find that the Vatican was the last organization or institution using them.
The details of the procedure were lost in the mid-19th century, as they were never publicized, and may not ever have been written down. {My personal speculation is that it involved the severing or removal of the vas deferens, although I’d be interested to hear opinions - especially contradicting ones - from one of the SD doctors.} Here’s a link which discusses castration in general terms, and the production of the castrato voice in particular.
A few years back there was a movie made about a castrato. I never saw it, but here’s a link to a page which will give more information and more links, including one to buy a copy of a digitally remastered recording of the voice of Allessandro Moreschi (1858-1922), the last of the castrati.
Here’s the Wikipedia page on it. And here’s another link: Who were the Castrati?
Of course, you could always Google it, as I did.
Some of the sites I looked at claimed that countertenors were practically the same as castrati. I seriously question this, as I knew two of them (father and son), and neither had significantly more volume than many sopranos I’ve known (myself emphatically included). Of course, there are some countertenors singing professionally who do have greater volume than most women singing in the same range, but on the basis of personal experience, I take leave to doubt whether the average countertenor (rare birds, to be sure) has volume similar to that of the castrati.
[sup]1[/sup]Having the ability to initiate intercourse was never the primary requirement; some hormone production was necessary in order to produce the volume and voice support one associates with the male voice throughout his range. Castratos were enormously popular with women who sought sex without the risk of pregnancy, although that was not a consideration with either those who created them, or those for whom they were created.