Burgruine Hohenburg auf Rosenberg is a ruined medieval castle probably erected in the late 11th century. The castle was first mentioned as castrum Hohenburc in an 1142 deed. It was then the seat of a Bavarian noble family, who as Counts of Lurn administered the Lurngau region within the Duchy of Carinthia. The last count, Altmann, had become Prince-Bishop of Trent in 1124, and upon his death in 1149, the castle was bequested to the Archbishopric of Salzburg and became the seat of episcopal ministeriales.
Under the mediation of Duke Ulrich III of Carinthia, in 1263 a division of the property was arranged between the Salzburg archbishops and the neighbouring Counts of Ortenburg, heirs of the extinct Counts of Lurn, who had aspired the Hohenburg estates for decades. In 1311 Archbishop Conrad IV of Salzburg enfeoffed a part of Hohenburg Castle to the sons of late Count Frederick I of Ortenburg (1247–1304). Nevertheless the residence became less important when it was replaced by nearby Feldsberg Castle as administrative seat of the Salzburg possessions. When the Ortenburg dynasty became extinct in 1418, their possessions passed to the Counts of Celje.
Today only ruins remain. The castle was probably destroyed in the 15th century conflicts between the Counts of Görz and the Habsburg emperor Frederick III over the heritage of Count Ulrich II of Celje. The former chapel was rebuilt as the Baroque St Mary's pilgrimage church (Maria in Hohenburg) in 1707.
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.