Ygritte: "Swords in the darkness"... Aye. The black brothers of the Night's Watch are that at least, as too many of the Free Folk know.
You southerners are strange. A man murders... and you train him to kill better. A man thieves or rapes and you send him where it's dark and private, well at least you make him promise to be good... and then you make him regret even that! From the time he's woken, to the time he's allowed to sleep he walks the frozen wall, carries frozen stones or boils frozen food. When he lies down at night he can't have anybody to warm his frozen bed. Well, not unless the crows like to... "nest" together. You think he remembers the stories they told him then? About when the White Walkerswoke in the Land of Always Winter and how the Wall and the Night's Watch were raised to stop them the next time - never mind trapping us on the other side).
We Free Folk have our stories, too. About how one of your king crows found something cold in the woods... with bright blue eyes. How he brought her home, through your wall, and declared himself "Night's King". For thirteen years he and his queen ruled over his brothers, making sacrifices as black as their cloaks. Lucky for you southerners, the Free Folk rallied to a King-Beyond-the-Wall, as we will when need be, and marched on the ancient castle he had taken as his own, the Nightfort. With the help of the Starks, we killed the demon and cleansed your precious watch. An' then they thanked us, an' kicked us back across the wall... as you always have.