With construction of the first fortification of the Prague Castle in the 11 th century, the place became the seat of Bohemian princes. The buildings belong to three different architectonic periods. There is the Romanesque palace built by Soběslav I around 1135, whose ruins are in the basement. Then there are palaces built by Přemysl Otakar II, King of Bohemia and Charles IV that were erected at the site of the old Romanesque palace. The upper ground, built under the reign of Vladislav Jagellion consists mostly of the Vladislav Hall. Under the Habsburgs, the castle was used as the seat of state offices, courts, and the Czech Parliament. In 1618, two imperial governors were thrown out of the high castle window. This incident is known as the second defenestration of Prague and it is supposed to be the initiation of the Thirty Years' War.