The ancient castle Castra Martis was built on a steep southern slope above the gorge of the Voynishka River at the end of the 3rd-beginning of the 4th century as part of the Danube Limes. It occupied a key position in guarding the important Roman road from Bononia to Singidunum (Belgrade).
In 408, the Huns under Uldin took control of the site during an attack on the Eastern Roman Empire, apparently by treachery. The fortification was reinforced under Justinian I, but was completely abandoned after the Gothic invasions in 586.
The fortress consisted of two parts: a small square fortification (quadriburgium) measuring 40x40 m, with powerful circuĀlar towers with a diameter of 12.5 m in the corners and a castle with the shape of an irregular quadrangle. It covered an area of 1.55 ha. The castle was accessible only from the south, where the gate was situated. Probably at the end of the 4th century, the protection of the gate was reinforced by the construction of another narrower wall.
Foundations of a Roman bath were discovered northwest.The quadriburgium is well-preserved and revealed in its entirety. Its fortress walls, built of stone and three-row brick girdĀers, are 2.2 m thick and 2 m tall, and the southeast tower rises to 16.3 m.
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.