The large pool – whose remains have been identified near the present Corso Bagni – was an important part of a huge spa complex dating back to the Roman Empire. Found in 1913 during the construction of the new porticoes, just south of the Hotel Nuove Terme, at the time the structure was only partially explored before being partly buried again and partly incorporated into the basement of the building then under construction. Further excavations carried out in the 1970s revealed the presence of other significant structures, such as to suggest an extension of the thermal complex northwards. However, only the latest research activities (performed ​​in 2001) led, finally, to a complete arrangement in plain view of the pool and to confirm the assumption of a wider extension of the thermal plant, of which the pool was a part.

In fact this complex covered, more likely, a substantial tract (probably up to the present Piazza Italia), but, unfortunately, it is mostly hidden or destroyed because of the continuity of settlement in the area in the modern age.

The spa building, along with the nearby amphitheatre (the exact location of which was identified in the 50s of the last century but that remains, to this day, completely unexplored), occupied a suburb of the ancient Aquae Statiellae, outside the Roman built-up area but easy to reach using the route of Via Aemilia Scauri.

The pool is rectangular shaped and of considerable size (13 metres x 6.5 metres). The tank is directly carved out of rock and closed around by a massive perimeter flaked stone wall that supported the roof. The access was possible on each side, since the whole perimeter wall surrounding it has three large steps, of different height, leading into the pool; the long sides of the pool are bordered by a wide corridor while along the short sides there is a very narrow passage. Originally, the space should have been covered by a mosaic clad vault made of glass paste tiles in various colours (found in large quantities during the excavations), with large windows protected by glass panes. The pool, maybe supplied directly by the water coming from the source “Bollente”, had to fulfil, within the thermal plant, the function of a large calidarium, that is to say an artificially heated space where people could take hot baths.

The pool was well-finished with materials of great value. The bottom and the steps of the pool were covered with slabs of white marble and other types of marble, whether or not coloured, decorated the above ground section: they often consisted of marble imported from Greece or Asia Minor.