SU 8231 is a basalt curb separating a 'porch' or 'sidewalk' (SU 8229) from the road to the south (as yet still unexcavated). It is thus also associated with the tufo step SU 8229 and the threshold SU 8201, and must have been in use in the imperial (or later) phases of the structure. In fact, the fact that the pavers are clearly repurposed from the road paving might suggest a relatively late construction, after some nearby roads had gone out of use.