Gorne and Gendel's War

"The brothers Gendel and Gorne, Kings-Beyond-the-Wall, went under the Wall through ancient caves buried deep in the Earth. But on the way back they took a wrong turn and were lost in in the darkness. People say that their children's children's children are still down there... looking for a way up, or for more food to find its way down."

- Samwell Tarly

Gorne and Gendel's War was an attempted invasion of The North by Kings-Beyond-the-Wall Gendel and Gorne, during the Age of the Hundred Kingdoms. Like all Free Folk invasions of The North, it was repulsed.

Battle
The invasion is remember more for the Free Folk retreat than the battle itself. The brothers Gorne and Gendel, who ruled together as Kings-Beyond-the-Wall, led an army of Free Folk through ancient caves. When the joint strength of the Night's Watch and the Kingdom of the North defeated the invasion, the kings attempted to retreat back beyond the wall through the same caves, only to get lost there forever.

In the books
The Free Folk initially managed to bypass the Night's Watch, only to run straight into the army of the King in the North. When learning that a battle was taking place, the Night's Watch intervened and helped the Stark army surround the Free Folk army. Together, they destroyed the invading army.

While Samwell Tarly claims that both kings got lost under the wall, the books specify that Gorne was confirmed killed, while Gendel may have escaped with his life. Northern traditions say he was killed with his brother, and the story told by Samwell is actually the Free Folk version of the events. Like many such legends, whether it happened or not is an open question.