His proposal included a large dome resting upon the width between the side aisles, which necessitated larger transepts and apses.

[citation needed] The nave contains twenty-two side chapels: Bologna was a principal center of Baroque music in Italy.

The musical organisation had been officially instituted by Pope Eugenius IV in 1436; the first regularly paid instrumentalists were added in the late sixteenth century, and in the seventeenth century San Petronio was renowned for its sacred instrumental and choral music, with its two great organs, completed in 1476 by Lorenzo da Prato and 1596 by Baldassarre Malamini, both still in remarkably original condition; the library remains a rich archival repository.

Three successive maestri di cappella marked the great age of music at San Petronio: Maurizio Cazzati (1657–71), Giovanni Paolo Colonna (1674–95) and Giacomo Antonio Perti (1696–1756).

[4] The current maestro, since 1996, is the harpsichordist Sergio Vartolo who has revitalised the cappella with a series of recordings for Naxos, Tactus, Brilliant Classics and Bongiovanni.

[5] The church hosts also a marking in the form of a meridian line inlaid in the paving of the left aisle in 1655; it was calculated and designed by the astronomer Giovanni Domenico Cassini, who was teaching astronomy at the University.

The position of the projected image along the line allows to determine accurately the daily altitude of the sun at noon, from which Cassini was able to calculate with unprecedented precision astronomical parameters such as the obliquity of the ecliptic, the duration of the tropical year and the timing of equinoxes and solstices.

On the other hand, the size of the projected sun's image, and in particular its rate of variation during the year, allowed Cassini the first experimental verification of Kepler's laws of planetary motion.

The terrorists planned to destroy the church because one of the chapels features a 15th-century fresco, painted by Giovanni da Modena and based on Dante Alighieri's Divine Comedy, depicting Muhammad in the eighth circle of Hell, in a section reserved for religious schismatics, being tortured and devoured by demons.