The term "Reichstag", when used to connote a diet, dates back to the Holy Roman Empire. The building was built for the Diet of the German Empire, which was succeeded by the Reichstag of the Weimar Republic. The latter would become the Reichstag of Nazi Germany, which left the building (and ceased to act as a parliament) after the 1933 fire and never returned, using the Kroll Opera House instead; the term "Reichstag" has not been used by German parliaments since World War II. In today's usage, the word "Reichstag" (Imperial Diet) refers mainly to the building, while "Bundestag" (Federal Diet) refers to the institution.