This wall is closely associated with the concave tufo slab drain in the western half of the complex (5600), generally belonging to the same phase, and, more specifically, part of the same design and function. It seems to form the northern wall of the channel of the drain in order to confine the water within the otherwise shallow waterway, and may have had a parallel wall on the south of the drain, which does not survive. At the eastern limit, before the opus reticulatum wall, these orthostat slabs turn sharply to the north, part of a design to accommodate the descent of the stairway to meet the slabs of the landing (5668). Given the lack of surviving features and stratigraphy to the north (between these slabs and the terracing cut in the bedrock), and the fact that the slab floor that is flush with the drain around the landing of the staircase does not continue any further west than the bend in the drain and slabs, two major questions remain, which are fundamental in reconstructing the use and appearance of the northern part of the middle terrace on this western side. Firstly, what was the nature of the space on the northern side of the wall? No traces of architecture or occupation remain. A retaining wall for the upper terrace, comparable to that on the eastern side of the complex, is impossible. With no gaps in these slabs, access at the level of the slab floor and drain to the northernmost part is also impossible. Large, deep cuts in the bedrock in that area in the eastern portion also suggest that a use surface is unlikely. Secondly, how and why does the space transition abruptly on the southern side of these orthostats from a paved slab surface to an irregular bedrock one, where it is physically impossible for slabs to have continued at a level flush with the drain? One of the few possible solutions to both of these questions is that west of the end of the slab floor and north of the orthostats, the level of the floor was significantly higher, and that the drain continued west under the floor level. Given that these orthostats seem to be insufficiently sturdy to support such a superstructure in themselves, something like a raised 'podium', with a solid core of stone blocks, might be hypothesized.

We do not know the purpose of this wall. Perhaps the wall contained a garden north of it. The wall and drain were constructed at the same time, as they run in a zigzag together. The wall also turns to accommodate the stairs (which are currently under the Opus Reticulatum wall.)Interestingly, there's no wall/drain combo on the other side of the complex, just a drain.