St. Mary's Church (Mariakyrkan) is the oldest still used building in Sigtuna. The brick-made church was constructed in the mid-13th century and inaugurated in 1247. It was, however, completed probably in 1255, when the archbishop Jarler was buried there. The church was enlarged and sacristy added in the 1280’s. Due the Reformation King Gustav Vasa ordered to demolish the adjacent abbey in 1530 and St. Mary's became a parish church.
The full restoration was made in the 1640’s and the present was added then. Mural paintings were restored between 1904-1905. There are couple medieval artifacts remaining in the church, like fonts, a triumph crucifix and small altarpiece.
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.