In the heart of Aosta, beneath Giovanni XXIII Square and adjacent to the Cathedral, lies the so-called Criptoportico Forense.

This place, dating back to the Augustan era, takes the form of a two-aisled gallery in the shape of a rectangular horseshoe, measuring 89m by 73m. It is open to the south and supported by a myriad of arches and plastered travertine blocks.

It is believed that this monumental structure delimited a sacred elevated area above the monument. However, its main purpose was certainly to serve as a containment and regularization structure for the terrain, as the area of Aosta where it is located had a slight slope. The presence of the Criptoportico helped level the sacred area and the forum square. Along with the criptoporticos of Reims, Arles, and Bavay (in France), as well as the one in Vicenza, the Aosta monument represents one of the few examples in the world of this type of architectural feature.

In particular, the Aosta example is considered a structure of great prestige because it was a place associated with imperial worship, religious or professional corporations of the city, and the self-celebration of local dignitaries.

For a long time, it was hypothesized that due to its particular physical shape, it could have been a military warehouse or granary. However, more recent studies have disproven this hypothesis and confirm the structural function of the monument. Nevertheless, during the medieval period, this place was actually used as a cellar.