Historical Castration and Voice Development: Understanding the Connection

Question
Hi... I am a little intrigue in knowing why in the ancient times, little boys were castrate in order to keep their voice...
What effect causes the castration in the voice?
THANKS!

Answer
Without testosterone, the boys didn't develope secondary male sexual characteristics.  These include a larger "voice box" (deep voice), pubic hair, chest hair, and beards.  

Castration would prevent the voice change because the voice box would not become larger.