In the year 1115, fortifications were erected at the site by Gosewijn I, Lord of Valkenburg. This original wooden keep survived until 1122 when it was destroyed under siege by Henry V, Holy Roman Emperor. The castle was rebuilt in the following centuries but was again destroyed in a siege, this time by Jan III, Duke of Brabant. The current ruins are those of the castle rebuilt in the 14th century.
The castle was blown up during the Franco-Dutch War, in 1672, by the army of King-Stadtholder Willem III to prevent it falling into French hands.
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.