The Municipal museums have a wide medieval section, where the frescoes removed from San Lorenzo church play an outstanding role. In effect, the higly remarkableStorie di santa Caterina(Stories about S.Catherine) constitute the main core of the frescoes coming from S. Lorenzo, and the story told by the frescoes is still wholly preserved. Such frescoes were originally located in S. Caterina chapel and may be attributed to a Master from Lombardy who was active in the last decade of the 14th century, conventionally known as Maestro di Santa Caterina (Santa Caterina master), since he wasn't a famous artist. Santa Caterina Master may have been trained at the Viscontis court, at the same time as Giovannino de' Grassi. Living in the context of late medieval courts, he probably dedicated himself not only to frescoes but also to miniature, as argued by some researchers. In effect, the cycle of Piacenza is strictly connected to an important illumination, the Libro d'Ore by Gian Galeazzo Visconti, now preserved in Florence National Library; such book constitues a useful chronological and stylistic term of comparison, since it approximately dates back to 1388. Other frescoes come from San Lorenzo's presbyterium; the most interesting one representsIncoronazione della Vergine (Coronation of the Virgin) andTrinitÓ (Trinity).As to this last work, researchers have made some hypothesis about its author, in order to define the original cultural contest it comes from. Boskovitz, for instance, has recently underlined the stylistic similarities between this fresco and the 1355 triptych belonging to Thyssen-Bornemisza collection. Thanks to such intuition, further research has allowed to define acorpus of works including the frescoesIncoronazione della Vergine(Coronation of the Virgin)andTrinitÓ(Trinity), presently at Palazzo Farnese,as well as the Thyssen triptych and other works, all originating from the workshop of Bartolomeo and Jacopino from Reggio, who were clearly very active in the area of Piacenza at the half of the 14th century.
The sculptures preserved in this section are also very remarkable. They witness a crucial moment in the stylistic development of romanesque sculpture between Wiligelmo and Benedetto Antelami, named by the critics"School of Piacenza". This expression appeared for the first time in a very important essay by Krautheimer-Hess (1928) with reference to a series of works, not only from Piacenza, characterized by the fusion of the stylistic elements of Wiligelmo and Niccol˛ we may find in the minor portals in the fašade of Piacenza's cathedral.Therefore, the twoProfeti (Prophets) (12th century) are very important, because their characteristics remind us of the style of the "School of Piacenza", as well as Majestas Domini (12th century), also belonging to the same cultural contest, and Madonna col Bambino (Madonna with Child) which was likely sculptured by a follower of Antelami and dates back to the first half of the 13th century.