This compilation shows some details, that I thought worth taking pictures of. The pictures use a picture, I have taken of the wall from close by, as background. The open space in the montage (below the statue of Triton [looks more like a green man]) shows something that someone carved into the brick at some stage. It is a rectangular (almost square), divided into 5 triangles; the letters P A at the top, right and an arrow pointing in the direction of the letters.
I just like that squinting lion, looking more scared than fierce.