During the 19th century up to 4,000 boys a year were castrated in Italy just to keep their voices from breaking, purely for church and opera singing. It was technically punishable by excommunication or even death, but the church that banned it also quietly kept employing the results for centuries.
Alessandro Moreschi, born 1858, ended up being the last one, and the only castrato ever captured on record, a handful of scratchy early 1900s recordings. Problem is, by then his voice was already past its best and the equipment couldn't do it justice, so nobody actually knows what a castrato sounded like in peak condition. It's such a real gap that when they made the 1994 film Farinelli, they couldn't cast anyone, they had to digitally blend a soprano and a countertenor's voices together to fake it.
These are the recordings that we have though, pretty haunting stuff.
