Friedrich II liked his architecture to mirror his political programme—Bebelplatz was designed to be a meeting place for science, art and political power. An academy, an opera house and a royal palace were planned, yet only the Opera House was finished in the king's lifetime. Later additions (the Royal Library and the Humboldt University buildings) are a testament to Freidrich's original project - all of them imposing classical buildings which unite to form one of Berlin's most impressive squares. Science and art are still represented; political power only to an extent - in the middle of the square an underground memorial (visible through a glass screen) bears testimony to the site where the Nazis burnt the books of political and philosophical opponents in May 1933.