One of the biggest mysteries from Game of Thrones has been revealed. 

In a new interview with the New York Post, GoT writer Dave Hill—who penned Season 8 premiere “Winterfell”—shared the significance of one of the show’s prominent symbols: the White Walkers’ spiral pattern.

Hill told the Post, “As we saw with Bran and the Three-Eyed Raven, the spiral pattern was sacred to the Children of the Forest, who created the Night King by sacrificing a captured man in a spiral ‘henge of stones.’ The Night King then adopted the symbol as a sort of blasphemy, like Satan with the upside-down cross.”

The symbol first appeared in the series’ pilot episode, when Night’s Watch rangers traveled beyond the Wall and found an encampment of dead people, whose bodies were organized into a rhombus with a line running through it. The spiral then appeared again, formed from dead horse parts.

The spiral becomes more important when Bran Stark witnesses the making of the Night King by the Children of the Forest at the center of a spiral, signifying that the threat of the Dead was conceived by the Children in their fight against the First Men.

While on the island of Dragonstone, Jon Snow and Daenerys Targaryen find cave drawings of these symbols as well, illustrating a past where the First Men and the Children of the Forest ultimately join forces and battle the Night King together.

The next episode of HBO's Game of Thrones arrives on April 21.