The archaeological investigations undertaken during the fourth excavation campaign continued to expose important topographic aspects of the Roman municipium of Trebiae, which were previously unknown or only partially known. The open area excavations concentrated on sector II.
As the research stands, it is difficult to identify with certainty the exact use and function of the structures that came to light. However, in light of their typology and construction technique, it may be suggested that they were structural elements relating to a Roman domus within a settlement with a long occupation period.

The understanding and interpretation of Room G is decidedly uncertain. This large room had a mosaic floor of pink and black tesserae depicting a marine scene with mythological figures, specifically nine large images arranged in a regular fashion on three registers. Depictions of animals such as deer, horse, bull and snake alternate with anthropomorphic figures, all with fish-like bodies; small winged cupids ride some of the animals. The floor is in a moderately good state of preservation and still in the study phase. Therefore, its chronological horizon remains to be defined, as does the room’s use. Although the marine iconography of the mosaic suggests this room was part of a bath complex, the total absence of architectural elements relating to water management seems to exclude this interpretation for the present.
The large corridor I was attached to room G. In fact, the corridor walls abutted the structures delimiting the large room with the mosaic floor. A threshold with sockets for a large double door was found at the point of contact between the two complexes. This appears to date to a period immediately after the creation of the mosaic floor in room G. Indeed, the threshold fills the gaps in the mosaic floor, meaning it post-dates the floor’s creation. At a slightly higher level, there was a beaten earth floor that seems to date to the early medieval period. In fact, the floor was in phase with the wall constituting the northern limit of corridor I. There was reused material in the wall; from the base in small blocks belonging to the Roman structure, the wall narrowed, as it got higher. This construction technique is recurrent in the early medieval period. Therefore, in this period the level of the corridor must have risen by a few centimeters with respect to the Roman floor level.

Room N is still in the excavation phase and its complete plan remains to be defined. The room is connected to rooms G, H, F and I. It also has a mosaic floor in pink and black tesserae forming a marine scene with mythological figures, specifically two large anthropomorphic figures of a triton and a nereid, framed by two registers of geometric motifs. Part of the mosaic floor remains to be excavated, thus the interpretation of the mosaic’s iconography remains to be completed. Once again, although the marine iconography of the mosaic suggests this room was part of a bath complex, the total absence of architectural elements relating to water management seems to exclude this interpretation for the present.

The preliminary study of the pottery, glass, and numismatic finds from the excavations documents occupation of the site between the 3rd century B.C. and the 7th century A.D. The preliminary analyses of the artefacts has made it possible to define a chronological series allowing the finds to be associated with the various structures identified.