User blog comment:Zippertrain85/Dawnguard Follow up./@comment-17114085-20131216013719/@comment-9062114-20131221203113

1) It's more likely there's a mist blocking it, as opposed to an invisible barrier. Even then, somebody's bound to have found it. People know what the Volkihar Vampire clan is after all.

2) That makes the most logical sense if you ask me.

The other points really don't matter now. If Skyrim has always been colonized, then Harkon couldn't have possibly been a king.