The Co-Cathedral of the Assumption of Mary was built in 1169 as a Romanesque basilica of a single nave on the foundations of a pagan temple of the fourth and fifth centuries, whose remains are still visible at the back of the sanctuary at about 1.5 meters deep. The façade and the south side of the cathedral, in the middle of the eighteenth century was decorated with Romanesque arches and brick niches. In the same period the church was expanded with the addition of two side aisles, altars and other works of art. During World War II the cathedral was severely damaged. The current appearance of the building is the result of the restoration executed between 1949 and 1950.
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.