Originally a free-standing structure, the Imperial Library (Hofbibliothek) was housed on the other side of the complex. Charles VI founded the library, which is now called the Prunksaal, cared for by the Austrian National Library (Österreichische Nationalbibliothek). Its construction was begun by Johann Bernhard Fischer von Erlach and finished by his son Joseph Emanuel in 1735. This magnificent hall contains the book collection of Prince Eugene, an enormous ceiling fresco by Daniel Gran, and statues of emperors by Paul Strudel making this part of the Hofburg its most significant in artistic terms. The exterior decoration with Attika figures was executed by Lorenzo Mattielli in 1726. He placed a statue of Pallas Athene riding on a quadriga above the main entrance. On the left portion of the roof, he situated Atlas, supporting the celestial globe, flanked by Astronomy and Astrology, and on the opposite side, Gaia with the terrestrial globe, flanked by allegories of Geometry and Geography.