The first church outside the walls that some scholars hypothesize to act as a cathedral, originally dedicated to the Saints Nabore and Felice and probably dating back to the 4th century, was destroyed in a fire in 906. It was then decided to rebuild the new cathedral within the selenite walls that protected a small portion of the remains of the Roman Bononia from the barbarian raids. The edifice near the Porta di San Cassiano, alongside an early Christian archdelago bell tower, elliptical in the base and round at the top, which is part of a preexisting cultural complex probably in the sixth century, must be placed between the X and the ' XI century. In a relief by Giuliano da Sangallo in the Vatican Library, related to a baptistery that stood in the immediate vicinity, it is clear that the octagonal planimetry, with four portals corresponding to the cardinal points and four apsidias, would almost coincide with the Baptistery of the Arians in Ravenna. This meant that the baptistery and the helicopter bell tower were part of a lost complex devoted to the cult of the Ariani coevo and that of Ravenna. The church measured 57 meters in length, but a fire burnt on August 1, 1141, injured her so seriously that it recommended her total reconstruction. The reconstruction and enlargement work was entrusted to Magister Albertus and the new cathedral was consecrated by Pope Lucius III in 1184. The new church, made of clay, was 70 meters long, 26,80 meters wide for 23 meters high and was presented in the typical Lombard-Emilian Romanesque style with three-sided high-rise façade, three naves with six-pointed arches supported by polystile pillars and three aps corresponding to the three naves. At the same time, the bell tower was raised from 31 meters to 40 meters. In 1220 Master Ventura, he started building a new marble portal on the south side of the church, the lion's door. Both Leandro Alberti and Vasari were very amazed and admired by this portal so much that Vasari himself, despite his famed aversion to medieval works, described it in the second edition of Life. Alberti reports that it was made up of two lions for red marble side, from which two columns ending in an arc lifted. Above it were two side-by-side telangas depicting a young man and an old man sitting on his chin, his hands resting on his crossed legs, which in turn supported the tortillary columns ending in a further bow. In the lunette there was carved the Christ with right San Pietro and left San Paolo. The ruinous earthquake that led to the collapse of the church roof in 1222 and the chapel roof in 1228 led the chapter to entrust new restorations to Maestro Tura, which ended in 1234. In the following years, Master Alberto erected the rosette on the façade door (1252) and the new main altar (1261). With the new great basilicas of the begging beggars orders that were being built and completed in the city, an increase in the size of the cathedral was imposed, which underwent several tampering and extensions over the course of the following centuries. In 1396 a tall porch was built on the façade, reconstructed between 1467 and 1500. Since 1477 there were works by the Ferrara painters Francesco del Cossa and Ercole de 'Roberti in the Garganelli Chapel; Their cycle of frescoes had considerable influence on Niccolò dell'Arca and Michelangelo. Behind the order of Cardinal Gabriele Paleotti, from 1575 the building was radically restructured inside, starting from the absidal side and the choir. The works were entrusted to Domenico Tibaldi before and to Pietro Fiorini then, but these modifications were so deep and so invasive that they had to collapse times in 1599.