The area under investigation is near the “G. Carreca” barracks in via Labicana. The research took the form of two excavation campaigns (2001-2002) and a survey using mechanical coring (2005-2006) inside the barracks and adjacent areas. The complex found presented a sequence of occupation phases and developed on two levels. The lower floor comprised a large rectangular room divided by three or four continuous rows of pillars, forming bays of circa 4.50 x 4.50 m to a maximum height of circa 6 m (at present nine are visible), covered by a series of depressed cross vaults. In the Roman period entry was via a flight of stairs from the upper floor, which ended in this room. On the steps of the staircase several brick stamps were found dating to the reign of Commodus (181-192). The room, whose characteristics seem to indicate that it was a large service structure, also acted as the substructure for the upper floor, where an extensive pavement in well finished opus signinum was found. In a subsequent phase, which has been given a preliminary date of between the second half of the 4th and the 5th century, the complex underwent large scale re-organisation, the access stairway to the lower room was blocked with a wall in opus listatum; at the same time this space was separated from the western part of the complex by the construction of a high wall, also in opus listatum. The re-organisation was completed by the creation of a large hall with an apse on a W-E alignment on the upper floor of the building. The excavation revealed a large part of the apse and a brief tract of the hall belonging to an almost intact building, already known to 16th and 17th century antiquarians, that is the church of SS. Marcellino e Pietro. Moreover, the coring surveys undertaken inside the building and the barrack’s square, aimed at identifying the size of the archaeological area and the nature and geo-mechanical characteristics of the walls present and of the terrain on which they stood, in order to formulate a strategic excavation programme and evaluate the depth of the archaeological deposit to be investigated, confirmed the exact position of the medieval church prior to its destruction in the 18th century. (Mariarosaria Barbera, Gianfranco De Rossi)