The results from the archaeological investigation undertaken during restoration work on Palazzo Guidobono provided a clearer definition of the occupation phases in the central area of Tortona, revealing a stratigraphy that developed from the early Roman to post-medieval period.
Period 1: Between the end of the 2nd – beginning of the 1st century B.C., the area seemed to have been used for production activities. There was evidence of clay quarrying and for a workshop area with numerous small kilns served by a channel that was gradually buried following the abandonment of production during the first half of the 1st century B.C. The area was then occupied by numerous middens and then sealed by various dumps of earth.

Period 2: at the time the nearby forum was created, the area was occupied by a large building, of which a few sections of partially robbed wall were identified, probably facing onto the urban stretch of the via Postumia that formed the decumanus maximus. After this building was demolished, earth dumps covered the area. A new phase of residential construction took place, attested by three houses divided by an open space with a well. The building technique, large dimensions, and high quality finishings suggest that these were prestigious buildings facing onto the decumanus maximus. The structures’ alignment places them within the urban layout of Dertona in the Caesarian-Augustan period.

Period 3: following a period of abandonment, an alluvial event occurred that partially covered the structures. Next, more modest structures, of perishable materials, were built on top of this level. These were soon abandoned and a substantial wall built, associated with a floor level, which crossed the area on a north-east/south-west alignment for at least 32 m. This was almost certainly a public building but this remains to be clarified.

Period 4: during the early medieval period the area was occupied by structures in perishable and reused materials, associated with beaten floor surfaces and a loose foundation, perhaps part of a modest house.

Following the abandonment of the small building, earth dumps formed the surface of an open area cut by holes. Subsequently, these dumps were cut by middens and the presence of charcoal was documented. The reconstruction of this area was attested by a brick wall on a north-west/south-east alignment, later cut by the east perimeter wall of Palazzo Guidobono.

Period 5: Palazzo Guidobono was built between the 14th-15th centuries.