The Altes Schloss or old castle, originally – since the 13th century – the heart of an extended hunting ground, surrounded by moats and equipped with numerous ancillary buildings, today forms an important visual motif in the gardens. It became a Habsburg possession in 1333 and was extended in the 17th century by Lodovico Burnacini.
After an attack by the Turks in 1683, this building was reconstructed in 1693 and another floor was added. Until World War I, together with the Blauer Hof, built in the 18th century, the Altes Schloss served as a spring residence for the Habsburgs.
References:The Clementinum is a historic complex of buildings in Prague. Until recently the complex hosted the National, University and Technical libraries, the City Library also being located nearby on Mariánské Náměstí. The Technical library and the Municipal library have moved to the Prague National Technical Library at Technická 6 since 2009. It is currently in use as the National Library of the Czech Republic.
Its history dates from the existence of a chapel dedicated to Saint Clement in the 11th century. A Dominican monastery was founded in the medieval period, which was transformed in 1556 to a Jesuit college. In 1622 the Jesuits transferred the library of Charles University to the Klementinum, and the college was merged with the University in 1654. The Jesuits remained until 1773, when the Klementinum was established as an observatory, library, and university by the Empress Maria Theresa of Austria.