The castrato voice was introduced in the 16th century, when women were banned from church choirs and the stage. ... The practice of castration, illegal and inhumane, produced an adult voice of extraordinary power attributable to the greater lung capacity and physical bulk of the adult male.

Who started the tradition of the castrato?

Castrati in the European Classical tradition

There were castrati in the court chapel at Munich by 1574, where the music director was Heinrich Schütz, and it is likely that Palestrina, director of the choir of St Peter's Rome from 1576 to 1594, would have been keen to emulate his famous contemporary.

Why was the castrato so important during Mass in church?

The Catholic Church's employment of castrati ran counter to canon law, which forbade the deliberate amputation of body parts except in the case of medical emergencies, but the popularity and skill of castrati singers was such that their existence was rationalized as a means of glorifying God through music.