Wagner doesn’t mean what it used to. Google “Wagner” today and you’ll be up to speed with the Russian private army’s exploits well before you read about Hitler’s favourite composer. In fact “Wagner” is as likely to suggest the 2010 X Factor contestant as the maverick German genius who, after handing out grenades on the Dresden barricades in 1848, sought to liberate opera from its Italianate shackles by means of Gesamtkunstwerk – or “total works of art” – and thereby free humans from lives of spiritless toil and demeaning leisure. Chief among Wagner’s total works of art is the 15-hour...