The Others built the Wall.

I could definitely see it having been forged "by ice and fire," whether literally or figuratively -- and most likely the latter, thousands of years ago. By this I mean, a pact was struck between the Children/WW and the First Men.

That pact resulted in the construction of the wall, which was intended as a largely symbolic marker between the lands promised to the Children and WWs to the North of the wall, and the lands promised to men South of the wall.

Obviously, some men either got caught on the wrong side of the wall's construction or chose to remain north and remain true to the old ways. These men eventually became the wildlings/free folk.

/r/gottheories Thread