The oldest part of the Ösmo Church was constructed in the latter part of the 12th century. The church was modernized in the 14th century, when the old chancel was demolished and replaced by one which was both taller and wider. The church largely gained its present appearance during the 15th century.
The interior of the church is decorated with frescoes added just after the middle of the 15th century. It is said that they were painted by Albertus Pictor, the most famous church artists of the medieval period. The church also contains a large number of coats of arms used in processions, and a triumphal crucifix.
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.