The Imperial Castle, the Hofburg, in the inner conurbation was for more than six centuries the seat of the ruler of Austria. From here the Habsburgs ruled until the end of the First World War in 1918. European history was written in this seat of power, from here Empress Maria Theresa carried out her policies and bemoaned the armed forces defeats against Prussia's Frederick the Great. It was here that Joseph II introduced his progressive alterations and Franz Joseph ruled for 68 years until the collapse of his empire. For two and a half centuries until 1806 it was the seat of the German Emperor and today it is the official seat of the Austrian Head of State. The complex consists of 10 key buildings and in them may be seen the manifestation of the 700- year-long architectural history of the Hofburg.