I believe this is the far East wall of the Forum of Augustus. It could be part of the Forum of Nerva or even Caesar, but there is a tall stone wall around the entire Forum of Augustus to protect the august temple from fire, a frequent problem in the Suburra, a slum in Augustus' time.
A view of a more recognizable part of the Forum of Augustus, the marble staircase in the center of the Forum. Note the Santissime Nome di Maria just to the left of center, and the big column (the Trajan Column) to the left of it. The brick arches along the left side of the photo support the modern road.
A closer look at the stairs.
People are still in the process of sorting through the rubble to reconstruct what once stood here.
http://www.uark.edu/ua/metis2/zanker/zanker_fig8.jpg
A drawing depicting the Forum of Augustus as it was.
It is almost hard to imagine the grandeur of this place as it must have been 2000 years ago. But the mind puts a fallen fragment of capital high over your head atop its column, sandled feet on gleaming new marble staircases, and the voices of shopkeepers drifting through the air.
But if you let the sun cast its shadows and squint a little, you can almost see it.
There was only a little space between the Forum of Augustus and the Forum of Caesar. The emporer Domitian decided to fill in the last area with another forum, which would serve mainly as a grand entry way to all the others. It was completed by Nerva, and thus bears his name.