While drawing 197 shows the design for niches only, drawing 198 also indicates the Antique vases and a box-shaped cinerary urn intended for the decoration of the Breakfast Room. Helen Dorey's essay on Pitzhanger suggests that Soane designed columbaria to imitate those found in the Roman catacombs, for the Breakfast Room at Pitzhanger. As Summerson suggests, the columbaria (defined as a series of niches to receive the ashes of the dead contained in cinerary urns) were to contribute to the sepulchral atmosphere of the room, along with the sombre colour scheme (although the colour scheme was different in the designs to the built version).

The influence of this scheme came in part from a visit Soane paid to Thomas Hope's House in Duchess Street. Hope's collection was chosen and arranged along similar lines. The influence of the Villa Negroni (presumably through the engravings of Angelo Campanella) has also been noted by Bianca De Divitiis. Moreover, Summerson suggests that the columbaria evident in drawings 197 to 198 and 203 to 205 were based on bodycolours by Charles-Louis Clerisseau, of which Soane owned at least five by 1800. In Summerson's opinion, even the domed ceiling of the Breakfast Room is an upside down form of the domed lids of cinerary urns displayed within the columbaria (also seen in the canopy-domed caps of the gated entrance).