Reggiolo’s historical centre developed in the vicinity of the medieval Rocca, a stronghold built around the tall 1242 tower, which later became its central donjon. For some time, the fortress was known as Castrum Novum (New Castle in Latin), to distinguish it from an older fortification located beyond the Tagliata Canal. The Rocca follows a quadrangular plan, with curtain walls approximately 40 metres long per side and four corner towers - two projecting from the southern sides, and two aligned with the northern walls -.

During the interventions commissioned by Ludovico I Gonzaga, the fortress was raised by about four to five metres, using materials recovered from the earlier Castrum Vetus (the Old Castle), the town’s original settlement. The main entrance opens at the centre of the façade, where traces of the former drawbridge and its defensive tower can still be seen. Inside the courtyard stands the central tower, whose restoration, around 1470, was entrusted to the Florentine architect Luca Fancelli. Built on a small artificial mound - known as “la mota” (Eng., the mud)-, the Rocca was once surrounded by wide moats. The Castle was never meant for residential use, serving instead as a military outpost. It remains one of the most representative examples of Italian fortified architecture, designed according to the “fence-castle” model typical of the Middle Ages, where the population could take refuge in times of danger. From the 1980s to May 2012, the Rocca hosted municipal art and cultural exhibitions.

Severely damaged during the 2012 earthquake, it is currently closed to the public, though restoration works have already been funded, with the aim of restoring its functionality and reinstating its role as a key cultural venue.