Donjon de Châteaumur is a dungeon built in the 12th century. An enclosure, either made of wood or stone, may have enclosed the keep in an almost circular area. What is certain is that, during this time, the keep was designed as an independent fortress, with a door located on the second floor and protected by a drawbridge that fit into the wall and the doorframe. The interior was divided into two by a partition wall for stability, and it had four levels: a basement and three floors with wooden floors. The ground floor stored provisions, the first floor housed the lord's residence (along with the drawbridge), featuring fireplaces and latrines, and the second floor likely had a guard room with access to the battlements. This top floor was accessible from the first floor via a spiral staircase embedded in the southeast buttress.
Perhaps in the 14th century, during the Hundred Years' War, an enclosure was added. Some parts of it are still visible because the houses around the keep's square are built against it, and there remains a fortified gate for carts. Another larger enclosure surely existed; one can see evidence, for example, just above the chapel's calvary. This could have been a wall or a palisade.
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.