The evening of the 25th of May 1869 was a special one for the people of Vienna. The new opera house of the city would open with a performance of Mozart’s Don Giovanni, attended by Emperor Franz Joseph and the King of Hanover. The building of the Staatsoper is a stunning 1.709 seat concert hall, built after the Renaissance Revival style. Inaugurated as the "Vienna Court Opera", its construction was commissioned by the Austrian Emperor and the result was a grandiose structure with state-of-the-art features and excellent acoustics. Great musicians were appointed directors here, including Gustav Mahler, who revolutionised the institution with his reforms and ideas. After the end of WWI, it was renamed Vienna State Opera and today it is also the home of the Vienna State Ballet and the site where the yearly Vienna Opera Ball takes place during the Carnival.