The building orientation is displaced compared to the traditional one, with the apse eastward which CVMA refers to for its numeration.

The most important and the largest church in Bologna is dedicated to St. Petronio, bishop of the town that lived in the V century and named its patron Saint. Once the Guelphs’ power in the town strengthened, a grandiose church was projected . Churches and streets still located  in the ancient Roman urban plan were demolished and on June 7^th  1390 the foundation stone was laid. The commission went to the master Antonio di Vincenzo (one among the experts consulted by the Fabbrica del Duomo in Milan on the cathedral works) that presented a woodened-walled 1/12 size model . The planovolumetric direction is faithful to the one projected by Antonio: it is divided in three naves where the central one consists of  six imposing bays, about 20 m each; the two side naves open into large chapels each doubled by walls put in.

The windows of the first chapels (mullioned of the flamboyant gothic type) correspond with the model by Antonio, while all the others are four-lancet windows.

At the beginning the works went on fast and the first four chapels of  both the side naves, the façade basement, the roofing, the provisional tribune and the altar  were completed by 1401. Antonio died in 1401 and the project was assigned to the sculptor Iacopo di Paolo. He  modified  the original plan for the façade simplifying the ornamentation in order to reduce the costs. 

The works, suspended for lack of funds, started again in 1419 when pope Martin V authorized to demolish some churches and the confiscation of their relative incomes. Yet, the works went on slowly: two chapels each side and the vaults together with some pillars, a temporary roofing and the bell tower  were executed between 1419 and 1440. In 1441 other two chapels, a new tribune, an altar and a new bell tower  were built; in 1477 the original project was realized with the last two bays. As for the vaults of the main nave not finished yet at the end of the XVI century, they were initially laid down  too low, then built up only in the years 1626-54 by Gerolamo Rainaldi.

The façade, with the wall hangings still unrefined at the top, the gate, framed by the Stories of the Genesis and of Christ’s  youth cycle, masterpiece of Jacopo della Quercia (1425-34).