Ancient stone walls of Athens Greece (5 replies)

I was recently in Athens Greece and near the Acropolis on the small hill opposite (near the Observatory) I discovered this ancient stone wall with very large stones, much in the style of other sites in South America. I wonder if Graham or others know about these walls and or their history ? They look far older and much bigger than I would have expected people to put there.
I dont know how to add pictures I have of them here but would if I could.