Fascinating article by Jan Swafford in Slate about the music of the castrati prompted by Cecilia Bartoli's new release, Sacrificium, featuring the music composed for the castrati. A quote from Swafford's article:
The [castrati] tradition rose from an unholy trinity of religion, money, and art. The church forbade women to sing in services. There was a standing ban, enforced primarily in the Papal States, on teaching women to sing professionally at all. Church choirs were staffed by boys, castrati, and adult tenors and basses. Meanwhile, in secular life, the greatest castrati, their virtuosity almost superhuman and their voices uniquely beautiful, were superstars of the opera stage and concert hall. As both singers and sexual toys, they were favorites of royalty and clergy, enjoying oceans of applause and cries of "Evviva il coltellino!" ("Long live the little knife!"). The presence of castrati in church music helped attract fans to services. On the opera stage, they played virile heroes and fiery heroines, competing for fame with the female divas of the day.