Construction of the St. Nicholas Church began about 1165. It is named after St. Nicholas, patron of travelers and merchants. It was built originally in the Romanesque style (with twin towers) but was extended and enlarged in the early 16th century in the Gothic style. The Baroque main tower was added in 1730; the portal dates from 1759.
From 1784 to 1797 the interior was remodeled by German architect Johann Carl Friedrich Dauthe in the Neoclassical style. The church has been a Protestant seat since 1539 after the Protestant Reformation, but today the Catholic Church is also allowed to use it.
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.