Built at the behest of the Cardinal Ercole Gonzaga and with the aid of Giulio Romano in his twilight years, the history of Mantua Cathedral dates back centuries. The early Christian churches of St. Peter and St. Paul were once situated to the left of where the edifice currently stands. Built in 804, these were the first churches in the diocese. It is believed that the ancient church of St. Peter's, which may have been built on the site of the Roman Forum, is the basis behind the artistic history of the present-day cathedral, which still presents a Gothic structure on the right-hand side and boasts a medieval bell tower. The interior, with its five towering aisles, was designed by Giulio Romano, who not only sought to evoke the basilicas of early Christianity in general, but also wanted to draw directly on pre-Renaissance St. Peter's in Rome. Needless to say, the church is replete with artworks from all eras, from the early Christian 4th century sarcophagus to the apse frescoes painted by Antonio Maria Viani.