Giuseppi Verdi's "Don Carlo" was a Behemoth, a lumbering monster. It featured variant openings, duets and trios and choruses to burn, ballet music that now only exists as a separate concert work, and most importantly, a great psychological/musical narrative frame -- the reason for all the elaboration and development.
What most of us know begins in a tomb in Spain and builds out an old and new subtext of European history, the battle of reactionary politics and the spirit of the Reformation. This background weaves this ideological struggle into a love story of great power.
There are essentially two versions of Don Carlo for Giuseppe Verdi. I don't mean that one is in French and the other Italian. Historians and musicologist are manic about the fact that this is untrue; however, there is a work, Don Carlos (francophone's are insistent on this), originally written in French for the Paris Opera that was so vast (5 hrs and change, they say), and it's richness so prodigal, that it obscured the works greatness.