Because of the presence of so many large tufo paving stones, it is possible that in an earlier phase, there had been another large paver in this space. At some point, the large paver may have been removed purposefully or robbed out and a suitable tufo replacement could not be placed for whatever reason such as cost or availability. In order to avoid having a large gap in the ramp, small tufo and basalt unworked stones were placed so that the ramp would still be usable. Alternatively, these stones represent some other feature- they could cover a sewer or drainage feature as the nearly travertine blocks do.