Currently visible in front of the museum is a small Roman funerary building that originally stood in the moat of the Punic-Roman fortifications of Murru Mannu. This was dug up and immediately dismantled in 1981 on the occasion of a static consolidation of the walls of the moat, and then it was transferred to Cabras.
The building includes a quadrangular mortuary room (3,82 m x 4,12 m x 3,88 m x 4,28 m), consisting of internal and external facing walls in blocks of sandstone, cemented with very poor lime; these walls are placed on a row of foundation made of sandstone blocks, one of which, evidently reutilized, still bears the symbol of an ax in relief. The floor is made of small and medium-sized rough stone bonded with mortar. The entrance to the room, open on the south side and helped by the presence of a block that is used as a step, has sandstone jambs and a threshold raised 55 cm higher than the floor inside.
In the northeast corner of the building there is an a cupa tomb, i.e. covered with semi-cylindrical elements, originally consisting of a rectangular base surmounted by a semi-cylindrical element made of stones cemented with lime, already violated in ancient time and so only partially preserved.
According to the excavator, C. Tronchetti, the a cupa tomb has never been used for burial; the deceased was in fact placed inside a sarcophagus in tuff stone placed beneath the floor of the building, at a depth of approximately 60 m in front of the same cupa. Inside the sarcophagus the deceased was buried, preserved only in the lower part of the body, with his head laying to the west and the feet to the east; the funeral goods were only a few fragments of Roman glass, perhaps related to unguentaria.
A coin of the Emperor Domitian, dated 88-89 AD, was discovered under the concrete floor; here, in the interstices of the blocks, was recovered a fragment of African Red Slip Ware (Form Hayes 3A) that suggested a chronology back to later than 90 AD. On the base of these findings and due to the presence of other tombs in the area related mostly to the late first century AD, it was suggested to date the funeral building at between the end of the 1st century AD and the beginning of the 2nd century AD.