The palace is a former Habsburg palace, and considered one of the 3 most important cultural buildings in Austria (the others being the Hofburg palace and Schönbrun palace in Vienna). It is the main building of a large residential complex used by the Habsburg dynasty. Construction started around 1460 under Archduke Sigismund, including medieval fortifications such as the Rumer Gate which was converted into the Heraldic Tower in 1499 under Emperor Maximilian I. The palace saw numerous expansions during the next 2.5 centuries. The most significant alterations were made between 1754 and 1773 under Empress Maria Theresia, who gave it a Baroque outlook. The palace now hosts 5 themed museum areas: Maria Theresia's Rooms from the 18th century, Empress Elisabeth's Apartment from the 19th century, a Furniture Museum, an Ancestral Gallery, and a Painting Gallery. The museum areas illustrate different aspects of the political and cultural history of the imperial palace under reign of the Habsburg dynasty for over 4.5 centuries.