Frederick had many famous buildings constructed in his capital Berlin, most of which still stand today, such as the Berlin State Opera, the Royal Library (today the State Library Berlin), St. Hedwig's Cathedral, and Prince Henry's Palace (now the site of Humboldt University). However, the king preferred spending his time in his summer residence at Potsdam, where he built the palace of Sanssouci, the most important work of Northern German Rococo. Sanssouci (French for "carefree" or "without worry"), was a refuge for Frederick. "Frederician Rococo" developed under Georg Wenzeslaus von Knobelsdorff.