Excavations at the north-eastern side of the city Cumae (modern Cuma) brought to light the Tomba del Banchetto per l’Eternità, a hypogeum chamber tomb with vaulted ceiling built in tuff blocks dated back to the first decades of the first century BCE. The exceptional nature of the discovery, resembling an Oscan tradition, is due to the peculiar decorative scheme, reporting a banquet scene and three funerary beds along with a table, reproducing a sort of triclinium. The investigation performed on decorated plasters, in situ by a spectroscopic approach and in-laboratory via minero-petrographic techniques, allowed us to infer the production technology of wall paintings and mortar-based support and the type of pigments used for decorating the tomb. The multi-layered plasters were made with specific mix designs in the different part of the tomb; similarly, different painting techniques were adopted according to the architectural scheme. In the lower part of the walls lime cocciopesto mortars adhere on the tuff blocks, likely to lend better hydraulic properties to the mortar-based supports in humid and wet environments. This part of the tomb, as well as the funerary beds, was painted in red using the fresco technique. On the other hand, in the upper part of walls and on the vault, the arriccio layer, containing volcanic sand, was covered with a thick and white intonachino layer composed of lime binder, constituting the support for the pictorial layer applied with a mezzo fresco technique. The investigation on pigments used for wall paintings points out to the use of a characteristic Roman palette, consisting of pure, natural and synthetic pigments (calcite, red and yellow ochre, haematite, organic black pigments, Egyptian blue) and skilful mixtures of colouring materials (mixture of yellow ochre and organic carbon black for the brown; mixture of kaolinite-rich clay, Egyptian blue and Fe oxides for grey; and mixture of organic—madder—and inorganic pigments for pink).