St Mary's Church was built inside Alabum, a Roman fort, on top of Llanfair Hill. A monastic cell from around 1126 was already on the site before building commenced. It is one of the largest medieval churches in the county, and has a substantial tower at the west end with a square stair-tower on its northeastern corner. The church is built of rubble stone with plain tiles on the roof. Earlier dressings are mostly in red sandstone, while nineteenth century dressings are in Bath stone. The nave and chancel are directly connected to the tower, to the porch on the south side and to the vestry and organ chamber on the north. The hymn writer William Williams Pantycelyn (1717–1791) is buried in the churchyard, where there is a memorial to him.
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.