The patron of Castelli is Saint Eusanius, celebrated on 8 May.
The municipality is famous for Castelli maiolica, a tradition dating back to the beginning of the Renaissance, although it is presumed to be earlier, which became famous worldwide for the quality of its design and above all for the finesse of its decoration: among the main masters are counted Antonio Lollo, the Grue and the Gentili, and Carlo Antonio Grue (1655-1723) is credited with the style that made Castelli maiolica famous, also through the work of his sons, in particular Aurelio Anselmo Grue; the works depicted mainly mythological themes or groups of armed knights. The town is home to the Museo delle ceramiche di Castelli (ceramics museum).
