The Hofburg in Vienna is the former Winter Imperial Residence. It was the Habsburgs' principal winter residence, as the Schönbrunn Palace was their preferred summer residence. From 1438 to 1583 and from 1612 to 1806, it was the seat of the kings and emperors of the Holy Roman Empire of the German Nation, thereafter the seat of the Emperor of Austria until 1918. Today it is the official seat of the Austrian Federal President. This complex of imperial edifices, the first of which was constructed in 1279, grew with the empire, and today the palace is virtually a city within a city. The earliest parts surround the Swiss Court, a courtyard named for the Swiss mercenaries who performed guard duty here. The Hofburg's styles, which are not always harmonious, result from each emperor's opting to add to or take away some of the work done by his predecessors. Called simply die Burg, or “the Palace,” by the Viennese, the Hofburg has withstood three major sieges and a great fire. Of its more than 2,600 rooms in 18 buildings, 54 staircases and 19 courts, fewer than two dozen rooms are open to the public.