In this case I wasn't thinking about the center rosette.
It isn't as definitely a fortification. The northeast
castle complex, which Colin Robson did refer to,
is of course more than the castle itself; it includes the
walls around the northeast rosette. The walls have a tower
on the south side of the northeast rosette.
I don't recall
anyone ever remarking on the northwest castle complex, which
is between the north and northwest rosettes. Note that it
does have a cylindrical tower.
I hesitate to mention this, but 'fortification imagery' is
sometimes seen in migraine aura. Kennedy
and Churchill thought that even the 'cannons' might be
migraine imagery. I do agree, though, that it is
quite a stretch to say this is proof that the VMs author
was a migraineur.