The Lime Kilns
The large circular pits visible in the forum area are lime kilns, used for “cooking” stones and marble to produce construction lime. The process involved prolonged heating at very high temperatures.
The pits could be simple or lined with masonry walls. The above-ground structure, now lost, would have resembled a dome.
These kilns provide evidence of the phases of spoliation of the ancient city. The earliest instances date back to the 6th century CE, though some kilns remained in use into the Middle Ages and the Renaissance.

Curiosity
All the architectural elements of the forum were either calcined or repurposed in later constructions. For instance, they can be seen reused in the walls of the Tappatino, the large building in front of you, as well as in other structures in the surrounding countryside and, notably, in the medieval settlements of the valley.