Olsborg Castle, also Olofsborg, was as a fortified castle located on a steep cliff, and might previous to later use been an early hill fort. It was constructed in 1503 or 1504 by the squire Nils Ragvaldsson from Åby, after a recent Swedish attack on Viken. Most of it was destroyed shortly after, when the commander of Bohus Fortress Otto Rud attacked on Christmas night 1504.
After the turmoil created by the dethronement of the Danish king Christian II, the Swedes returned, seized the area and reconstructed Olsborg's fortifications. The brief Swedish rule of northern Bohuslän was administrated from Olsborg by the nobles Lars Siggesson (Sparre) and Ture Jönsson (Tre Rosor), between 1523 and 1525. In 1525, the administration was moved to Karlsborg Castle, south of Hamburgsund. During these years, the castle defenses were improved, especially in 1526. During Christian II's attempt to retake his throne, the part of Bohuslän under Swedish rule was attacked, and both Karlsborg and Olsborg were destroyed by Norwegian forces in December 1531.
Decades later, several attempts to rebuild the castle was made by Sweden. Eric XIV in 1564 and Johan III in 1569 and 1570 both tried, but the attempts were unsuccessful and the castle remained in ruins. The ruins were still clearly visible during the early 20th century, when they were excavated by Wilhelm Berg, who also excavated other castles in the province, such as Ragnhildsholmen Castle and Dynge Castle.
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.