Thanks for that link baz.

Barbrook II looks so like a corral that I'm tempted to say that it was a corral :-) I'm not saying of course that all circles were corrals I'm saying that some may have been, and what we now see just as a circle of standing stones may have once had walls or fences between the stones.

As I said above, I'm happy to be proved wrong, but I do think the conjecture is worth considering (and perhaps keeping in mind when we visit circles as someone might spot something that might reinforce the conjecture).