The first planetarium in Rome, opened on October 28, 1928, and in operation until the 1980s, was housed in an ancient building from the 3rd century and was unique in this respect. The Zeiss Planetarium with its 19.6-m dome was located in the Aula Ottagona, part of the complex of the ancient Baths of Diocletian. Originating as a thermal building in ancient Rome, it has performed very different functions over the centuries. Here, for the first time, the projection dome was integrated into an existing building, under the huge ancient vaulted ceiling. Inside the planetarium was arranged in such a way that it did not alter the large Roman vaulted ceiling but allowed for a view of it in the annular space between the old and new structures. The steel network dome support structure still exists today in the new Museum of Rescued Art and provides an effective contrast to the stone vaulted ceiling. The Zeiss projector was not on wheels as usual but was fixed in place. The planetarium hall could seat 370 people. The main entrance on the Via Romita still bears the inscription "Planetario". The projector also survived and is on display at the Astronomy Museum in Rome.