The Château de Lacassagne is thought to date from the latter half of the 15th century, with additions and alterations made in every century until the 19th century. It originated as an ancient salle (hall) and was altered in the 15th century with the addition of a spiral staircase and windows. A residence was added in the 17th century. On the first floor, in a room known as the Salle des Chevaliers de Malte, the painted decor was done between 1620 and 1640 for Jean Bertrand de Luppé, prior of St Gilles, and intended as a replica of the grand council hall of the Knights of St John of Malta. Among the pictures are copies of Matteo da Leccio's paintings representing the attack on Valletta by the Turks in 1565. The originals were in the council chamber of the Grandmaster's Palace in Valletta, Malta and were destroyed by Napoleon Bonaparte in 1798.
In the 19th century, a west wing was added to the main building. The castle is not open to the public.
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.