Well, I`m not abandoning my ill-thought out theory yet. :o)
What function does a ditch perform, other than being a barrier to humans or animals? I suppose you could fill it with water, although I don`t see why.
As far as I can see, a steep-sided ditch, dug into the bedrock, would be an effective barrier (to animals) as long as it`s wide enough not to be able to jump across.
As far as it being a danger to animals falling in, I presume that it would be even worse when a human fell in.
>What advantage would a henge have over just a fence or stockade or something?
Err......you could stand on the bank and keep an eye on everything within the henge.
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