The Duomo museum is to be created in the cathedral’s undercroft, with an itinerary which will show the remains of the crypt of S. Maria del Popolo (Romanesque cathedral) and the various construction phases of the complex. In the crypt area an opus signinum pavement has emerged connected to three rooms, perhaps service areas created following the crypt’s abandonment in the second half of the 14th century, when the deconsecration of the church lead to the creation of houses and workshops in the area. In the zone corresponding to the Romanesque cathedral’s north nave three segments of a mosaic, the remains of a trilobed pilaster of Romanesque date have been uncovered. A concentration of structures overlying the mosaic relating to the various phases of construction and abandonment of the church has also been brought to light. Several structures in the east and west areas of the excavation belong to the earliest phase, however only a minimal part can be documented. A substantial structure constructed in small to medium sized cobbles and brick fragments, perhaps part of the pre-Romanesque cathedral, dates to the second phase. Subsequently, the Romanesque church was built (end of the 11th-12 century), paved with a polychrome mosaic, which has been lifted for restoration. A panel with an allegorical scene of a goat whipping (?) a four-legged animal tied to a post. Below, separated by a border is a second panel in which appears the head of a man wearing a hat. In another two fragments there are graduated, zig-zag and plaited motifs; below are floral motifs (and perhaps other figured scenes) delimited on the left by a border of triangular marble crustae. In the following period the mosaic was obliterated by a layer of mortar and the central area cut by three walls in a north-south direction. Subsequently, the walls closing the space to the north were built perhaps to create service rooms following the deconsecration of S. Maria del Popolo at the time of Cardinal Ippolito de’Rossi. These walls are still visible. In the extreme eastern area a barrel vaulted tomb was built. The pilaster standing at the eastern end of the excavation dates to 1759. The last intervention relates to the construction of the pilaster to the north-west (1852-1855). (R. Invernizzi – M. C. Ceriotti)