Kastellet is one of the best preserved star fortresses in Northern Europe. It is constructed in the form of a pentagram with bastions at its corners. Kastellet was continuous with the ring of bastioned ramparts which used to encircle Copenhagen but of which only the ramparts of Christianshavn remain today.
King Christian IV of Denmark initiated Kastellet’s construction in 1626 with the building of an advanced post, the Sankt Annæ Skanse (St. Anne's Redoubt), on the coast north of the city. The redoubt guarded the entrance to the port, together with a blockhouse that was constructed north of Christianshavn, which had just been founded on the other side of the strait between Zealand and Amager. At that time the fortifications only reached as far north as present day Nørreport station, and then returned south east to meet the coast at Bremerholm, the Royal Shipyard. However, part of the king's plan was to expand the area of the fortified city by abandoning the old East Rampart and instead extend the rampart straight north to connect it to Sankt Annæ Skanse. This plan was not completed until the mid-1640s, shortly after King Frederick III succeeded King Christian IV.
After the Swedish siege on Copenhagen (1658–1660) the Dutch engineer Henrik Rüse was called in to help rebuild and extend the construction. The fortification was named Citadellet Frederikshavn ('The Frederikshavn Citadel'), but it is better known as Kastellet ('the citadel').
Kastellet was part of the defense of Copenhagen against England in the Battle of Copenhagen (1807). During the German invasion of Denmark on 9 April 1940, German troops landing at the nearby harbor captured The Citadel with very little resistance, thereby forcing the Danish government to surrender.
Kastellet was renovated 1989–1999 with funds from the A.P. Møller and Wife Chastine McKinney Møllers General Fund.
A number of buildings are located within the grounds of Kastellet, including a church as well as a windmill. The area houses various military activities but its mainly serves as a public park and a historic site.
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.