The Thirteen have spoken.
Game of Thrones Season 2, Episode 4
I've demanded a meeting of the Thirteen.
One of them did this or knows who did.
Game of Thrones Season 2, Episode 7
HARALDSON: What age are you, boy?
Thirteen.
Vikings Season 1, Episode 3
Thirteen. Do I have 14?
Game of Thrones Season 5, Episode 7
It was given to me by the Thirteen.
Game of Thrones Season 2, Episode 4