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.