As moats go, it’s pretty inconsequential. Personally, I think it was just a matter of Graham showing off his digging-in-a-straight-line skills. But any marauder worthy of the name wouldn’t even need a horse to jump it. I can do it myself and my marauding skills are rubbish.
And call this a drawbridge? It doesn’t even lead to the front door:
At a rough guess, I’d say someone was having a laugh.