The literary sources provide little information about the town of Trebiae, which became a municipium in 90 B.C., governed by a college of quattuorviri. In the Augustan period, the town, whose inhabitants probably belonged to the tribe of the Oufentina, was included in the Regio VI. In the early medieval period the town’s close relationship with the eastern branch of the via Flaminia increased its strategic importance and in about the 7th century it became seat of the gastald of the Lombard Duchy of Spoleto.

Structural remains of Trebiae emerged in 1980, during the construction of a railway underpass situated at only 50 m from the church of S. Maria di Pietrarossa. The houses faced onto a road with drains. An enormous cippus of local limestone was found inside one of the houses. Perhaps a statue base, it bore a dedication to Jupiter Optimus Maximus and can be dated to about the 2nd century B.C. In 2005, work on the construction of a public building at 150 m from the church led to the discovery of about 15 burials in stone coffins, datable to between the second half of the 6th century and the mid 7th century A.D.

The first season’s excavations (2015) outlined and documented important previously unknown or only partially known topographical aspects of the Roman municipium of Trebiae. Work concentrated on two sectors denominated I and II.
Two walls were intercepted in sector I, at a right angle to each other, probably relating to a late antique-early medieval phase. At present, their original plan is unknown but they appeared to be associated with an area used for activities involving the reuse of various types of materials, such as metals, glass and marble attested by the presence of waste materials and scraps.

In sector II, a well-built wall, probably belonging to a Roman domus, was uncovered. It was faced with polychrome wall plaster on both sides and was therefore a dividing wall between two rooms, whose original extension is at present unknown. The rooms were only partially visible, but each had a well-preserved floor. One was constituted by waterproof opus signinum, the other was a mosaic decorated with a plait motif of red and black tesserae on a white background that borders a central field whose decoration is not yet visible.

The preliminary study of the pottery, glass, and coins indicates that the site was occupied between the 2nd and 7th centuries A.D. A preliminary study of the artefacts has produced a chronological seriation that associates the finds to the various structures identified.