This is one of the grandest baroque libraries in the world, a cathedral of books, its centerpiece the spectacular Prunksaal—the Grand Hall—which probably contains more book treasures than any comparable collection outside the Vatican. The main entrance to the ornate reading room is in the left corner of Josefsplatz. Designed by Fischer von Erlach the Elder just before his death in 1723 and completed by his son, the Grand Hall is full-blown high baroque, with trompe-l'oeil ceiling frescoes by Daniel Gran. Twice a year, special exhibits highlight some of the finest and rarest tomes, well documented in German and English. From 1782 Mozart performed here regularly at the Sunday matinees of Baron Gottfried van Swieten, who lived in a suite of rooms in the grand, palacelike library. Four years later the baron founded the Society of Associated Cavaliers, which set up oratorio performances with Mozart acting as conductor. Across the street at Palais Palffy Mozart reportedly first performed The Marriage of Figaro before a select, private audience to see if it would pass the court censor.