Breeches role
Breeches roles are usually female singers acting the role of a young man. They are normally sung by mezzo-sopranos or contraltos with light voices because they can often sound boyish. In the 17th and 18th centuries it was normal to have actors and actresses who cross-dressed. It was the time when castrato singers were popular. These castrati were men pretending to be women, but there were also women pretending to be men (especially when the actress was trying to deceive another character) and the audiences were used to this kind of thing. As they gradually stopped the horrible practice of castrating young boys in the late 18th century these male characters started to be sung by mezzo-sopranos instead.