As part of the work in the Basilica Noniana, a Bourbon _cuniculus_ was excavated for a length of 25 m. From documentary sources it is known that it ran for circa 110 m along the _decumanus maximus_ as far as the theatre. In this phase of the investigations, the emptying of the _cuniculus_ was undertaken in order to gain some idea of time and method which would help with the planning of a subsequent excavation of its entire length. In fact, the complete emptying of the structure, as well as creating an interesting underground link between the theatre and the open-air sector of the archaeological park, would consent improved aeration, probably forced, with a good probability of lowering the concentration of radon gas detected in the theatre. Moreover, from a scientific point of view, the intervention would permit the recovery of important topographical data regarding the relationship between the _Basilica Noniana_ and the buildings or spaces around it and in relation to the fundamental problem of identifying the forum. The first few metres of the _cuniculus_ had an irregular line, with the presence of offshoots and widening at the sides relating to the exploration and removal of the marbles from the remains of the four-faced arch which stood in front of the basilica and which, following the 79 A.D. eruption, collapsed onto the latter’s façade. The excavation also revealed that the entire area in front of the _Augusteum_ and the basilica had been persistently explored both by the Bourbon excavations and in earlier periods. The emptying of the _cuniculi_, undertaken for the first time using stratigraphical excavation, showed that the area had been crossed by tunnels in three different phases, at different levels and of different sizes. The investigation of this sector provided important confirmation of Bellicard’s plan, which placed a porticoed area to the north of the quadrifrons arch which is very similar to that visible today on the south side of the _decumanus maximus_. In fact, having crossed the _decumanus_ the _cuniculus_ seems to align itself along the latter’s west sidewalk, at the base of which ran a small channel for rainwater collection. The sidewalk had a kerb of parallelepiped tufa blocks, on which the portico columns rested, whilst the ambulatory was paved in _opus signinum_. The columns were built of _opus testaceum_ faced with red plaster on the lower third, whilst the upper part showed no traces of any facing. The excavation also identified a second column, and thus it was possible to calculate the spacing (circa 2.50 m). The emptying of this _cuniculus_ went well beyond expectations in providing data relating to the difficulties and time necessary for a complete excavation of the remaining 85 metres leading to the theatre. The work also confirmed the existence of a portico along the _decumanus_ north of the basilica, showing once again the quality of the recording undertaken in the 18th century through the exploration of the _cuniculi_.