Under the museum are located a number of architecture pieces, once part of the town's main buildings. Among these the "Capitolium", a temple whose massive dimension can still be hinted at from the remains of its "podium" (basement), covered with stone blocks dressed in shell mortar and coated with stucco. The "Capitolium" was devoted to the triad Jupiter-Giuno-Minerva, and was modified during the first centuries a. C. following Hellenistic criteria; the wooden structures were replaced with stone elements and a portico with Doric and Ionic pillars was added. A large section of the museum is devoted to the "Capitolium" temple and to its evolution through the centuries.

A great number of parietal decorations were found in two buildings, which were consequently named "the Fresco House" and "the Mosaic House". In the first, a number of important frescos from the Clodio-Nero period were brought back to their splendor by a careful restoration work: on the north side of the building, different fragments were linked together into nine meters of flower decoration on a black background. In the Mosaic House, late republican (I century b. C.) mosaics embellish the floors: in a characteristic Roman style, they depict the "Circo Massimo" in Rome, Hercules, dancing scenes, flowers and birds.