Wagner was never truly happy with his opera, Tannhäuser.  In fact, he penned two different versions:  the first is referred to as the Dresden version (or the original), and the second is referred to as the Paris version.  Wagner reworked the opera following its Dresden premier since it did not elicit the response for which he was hoping.  In the Paris version, Wagner wrote in a bacchanalian ballet within the first act to represent the revels of the goddess, Venus, as well as a few other slight changes.  Despite his edits, the performances were not received well in Paris either.  However, the Paris version is what remains largely performed to this day.  Read the synopsis of Wagner's Tannhäuser.