One of the tangential pleasures of opera-going is the insight it affords into how very, very bad nineteenth-century theatre must have been. If it weren’t for opera, the likes of Victorien Sardou (Tosca), Maurice Maeterlinck (Pelléas et Mélisande) and David Belasco (Madama Butterfly) would be rightly forgotten. Even Victor Hugo’s plays would be history without Rigoletto. But opera rescued their work from drabness and transformed it into something iconic, universal.