https://m.reddit.com/r/asoiaf/commen...t_nights_king/
Pretty lengthy theory, but raises some interesting questions. Was the wall built to keep humans, alive during the Age of Heroes, out of the North?
I want to spin off of this: was the Night's Watch originally manned by Others to keep humans on the southern side of the wall? Once the Night's King was banished from the Wall it was established that no fort should be built blocking the south's access to the wall to maintain an access to the Night's Watch. This would also explain the division of the Night's Watch from the Seven Kingdoms. That would explain the 13 Lord Commanders potentially being White Walkers as well.
Far out there, but interesting.