It has been mentioned that in Trench I there is evidence of three successive stages of these defences.
“I'm looking for a feel and I have to find what that feel is before I can move on from there. I'm not necessarily catching stuff in such a simple way - I don't need to. So, I'm going for something else.”
“But primitive man had enemies real as well as imaginary, and they were not subject to priestly sorceries.”