SU appears to be a dump of unwanted material, given the range of inclusion types (plaster, pottery, bone, iron nails, lead slag, tesserae, marble and basalt) set within a square feature of badly preserved mortar, of which the corners most fully survive. There are moderate to frequent inclusions of a white mortar which likely belongs to the SU below. Given this it seems plausible to suggest this fill may have been deposited in some sort of plastered or mortared basin. The inclusion of many large stones of basalt within this deposit may have largely broken up the plastered sides/floor of the basin, resulting in the commingled interface between this SU and the one below, and the inclusion of fragments of mortar in SU8149.