http://thesmartset.com/article/article0806070116.aspx
I have always found it very interesting how castrati were "created" and used.
You can hear a castrati singing here
Today, anyone curious about the castrati’s unique voices can listen to a recording made in 1902 by the very last of the breed, Alessandro Moreschi (1858-1922).
http://thesmartset.com/files/audio/AMoreschi.mp3