The Marble Hall, the most breathtaking room of Upper Belvedere, is located in the centre of the first floor of the palace. A masterpiece of Baroque interior architecture, it was here on 15 May 1955 that the Austrian foreign minister Leopold Figl and the representatives of the four signatories signed the Austrian State Treaty.
 
From the balcony of this hall, where Leopold Figl showed the State Treaty to the people of Vienna with the historic word "Austria is free", the probably most famous view of Vienna can be enjoyed. Around 1760 this view was captured by Bernado Bellotto (1721-1780) in one of his renowned paintings.