The former Jesuit College, and with its 20 000 square meters the second largest built-up extension in Prague after the Prague Castle. The Jesuits were invited to Prague by the Habsburg dynasty in 1556 to help strengthen the position of the Catholic church in Bohemia, a country divided in terms of religion. The builders of this great work were Francesco Caratti and František Maxmilián Kanka. Nowadays, there lies, inside the Clementinum, the National Library of the Czech Republic with more than 6 million volumes, 6,000 manuscripts and 4,000 incunabula. Very beautiful is the Library Hall of the Jesuits, with a fresco by Jan Hiebl from 1727. The Old Refectory of the Jesuits is used, today, as the Reading and Study Room. It's really very impressive. We also emphasize the Chapel of Mirrors and the Mozart Hall. These rooms are used currently as concert halls thanks to their very good acoustics.