Klementinum is a large complex of buildings in Prague, consisting of churches, astronomical tower and a library. It is the first college in Prague where the Jesuits came in 1556. Ferdinand I called them up to Prague in order to help him in his Counter-Reformation effort. After arrival, they settled in a former Dominican monastery of St. Clement in the Old Town (Staré M?sto) next to the Charles Bridge (Karl?v most). This small church later gave a name to the entire complex – Klementinum. When the Jesuit Order was dissolved and the Jesuits had to leave Prague in 1773, the Klementinum complex was taken over by Prague University and the National Library. It is the largest complex of buildings in Prague, after Prague castle, including the Church of St. Clemens and the Church of St. Salvator. The walls of the Baroque fortress enclosed a college, schools, churches, a library, a theatre, an observatory and a printing shop. Concerts are often held in the Mirror Chapel (1724-30).

One of the most amazing buildings in the complex is the Baroque library hall which was finished in 1722. Its appearance and arrangement – for example the labels on library bookcases – survive intact. Thus it provides us with an example of the setting of an authentic Baroque library. The books in this hall constitute a collection of printed theological literature written in all languages except Czech, gathered as they were arriving at the Klementinum from 1600 until recent times. The books with whitened backs and red marks have been there all along since the Jesuit period. The ceiling decoration, created by Jan Hiebl, symbolizes the antique wisdom and learning as the basis which leads to Biblical prophets and later to Christian teachings.

On the sides there are profiles of significant Jesuits and at the head of the library there is a painting of Joseph II, who enriched the Klementinum library with confiscated properties of abolished monastic libraries. Around the walls there is a gallery with a balcony with a forged railing. In the middle of the hall are placed ancient globes. According to the legend, the Jesuits brought with them a single book upon their arrival, but when they finish building the library, they had 20.000 volumes. As early as in 1777, the library was opened to the public as the Imperial and Royal Public and University Library. The library collections were rapidly growing. From 1782, all Prague printers had to hand in obligatory copies and after 25 years, this obligation spread to the entire territory of the Czech lands.

Today, the library is in use as the National library and has over 6 million books. The oldest book is the Vyšehrad Codex (Vyšehradský kodex), there is the Chronicle of Dalimil (Dalimilova kronika) in a pocket edition and there are books on dogmatics, hermetics, numerology and many other rare volumes.

Interestingly, the oldest weather recording in the area of the Czech lands started in Klementinum in the year 1775. The recording continues through the present day.