This small theatre is located in the piano nobile of Palazzo Montalto, thus called after the birth-place of its founder, Pope Sistus V, who at the end of the 16th century turned it as a university boarding school for young students from the Marches region.  This function continued until the French revolution, to start anew in 1873 by today's Collegio San Luigi, previously known as Collegio dei Nobili under the Barnabite Brothers. In the private residence the area now occupied by the theatre is thought to have been in use as an elegant reception hall for balls and parties, as it is provided with a gallery for the orchestra.  In 1879 the project by F. Gualandi for its use as a theatre was completed. Its rectangular layout is livened on three sides by a running gallery supported by scrolled brackets. A balcony (no longer in use) opens up on the side facing the stage, with a five-arch loggia supported by slender pillars. An eclectic-style decoration made by A. Guardassoni and G. Minelli livens up the ceiling subdivided into three oval medallions with flower bunches and the allegory of Fame in the centre.  Right in the middle of the fillet over the stage the insignia of Collegio can be seen (a ship tossed by storm with the Latin words Propere et Prospere) flanked by two figures of youths.  Today, the theatre, which is dedicated to the Bolognese artist A. Guardassoni, is used for the educational activities of the college with conferences, lectures and, occasionally, charity events.