shell with a thickness of 57 mm (2.24 in), allowing natural light to fill the exhibition halls. The Arts Hall opened on December 1, 1938 with A Half Century of Croatian Art, a major retrospective exhibition. Mosque The pavilion functioned as an art gallery for only three years before it was turned into a mosque in 1941, at the beginning of World War II, as a gesture of the Independent State of Croatia towards Bosnian and Croatian Muslims. Architect Zvonimir Požgaj headed the project for adapting the interior of the pavilion to better suit the functions of a mosque, and Stjepan Planić designed the exterior of the mosque. Požgaj significantly altered the interior of the pavilion, introducing a new ceiling of iron and concrete underneath the original ceiling to solve the problem of temperature and acoustics. According to Planić's plans, three minarets measuring 45 m (147.6 ft) in height were placed around the pavilion, but the exterior of the building was not altered. Planić also added a fountain flanked by benches in front of the building’s main entrance. The interior of the mosque was decorated with stucco patterns based on early Croatian ribbon motifs created by the sculptors Botuhinski, Brill, Ivanković, Jean, Loboda, Lozica, Matijević, Papić, Penić, Perić, Radauš, Štigler, and Turkalj. The mosque was inaugurated on 18 July 1944 and functioned until 1945. In 1949, the minarets were demolished and the interior decor was removed to make way for the new Museum of the Revolution. The Museum of the Revolution Architect Vjenceslav Richter headed the project to design the Museum of the Revolution, which was to display documents pertaining to Partisan battles during World War II. Richter added an additional floor and new staircases to the interior space and constructed new walls to hide its circular form. All of Richter’s additions were designed to attach to the original structure, so that they could be removed without harming the building’s interior. The Museum of the Revolution officially opened on April 15, 1955. Restoration and renovation By the mid-1980s, discussions about the function of the pavilion had resumed, and in 1988, the curators of the Museum of the Revolution invited architects Ivan Crnković and Dubravka Kisić to draw up a study on the feasibility of restoring the pavilion to its original form. In May 1990, the Croatian Association of Artists (HDLU), headed by Ante Rašić, organized the exhibition Dokumenti-Argumenti to present