La Platte Mare is a simple megalithic chamber with a single capstone dating back to the Chalcolithic or Early Bronze Age (2500 - 1800 BC). Early drawings show that some stones have been disturbed. Traces of a surrounding circle of stones 5m in diameter are no longer visible. One stone has a curved row of 12 cup marks though only 7 are visible above ground. A few metres away are the remains of another possible cist or chamber.
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.