Torsburgen was the largest ancient fortress in Northern Europe. It was originally constructed at the beginning of the 1st century AD. It was reinforced during the 4th century and used until c. 1100 AD. A timber-laced stone rampart encircles an area of 12 hectares. Scholars estimate that nearly 1000 soldiers would have been needed to defend it and it could have been providing refuge to the entire population of Gotland that is calculated to be between 6,000 and 10,000 in the early medieval period.
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.