When was the practice of castrating choir boys commenced by the Vatican commenced and when was it abolished/?

The number of castrati declined during the 19th century. In 1870, castrations were banned in the Papal States -- the last political jurisdiction to do so. In 1878, Pope Leo XIII prohibited the hiring of new castrati by the church. By 1900 there were only 16 castrati singing in the Sistine Chapel and other Catholic choirs in Europe. In 1902, Pope Leo XIII ruled that new castrati would not be admitted to the Sistine Chapel. In 1903, Pope Pius X formally banned adult male sopranos from the Vatican. The Church's last castrati, Alessandro Moreschi, died in 1922.

castrated choir boys, ~1500 to 1903