What Is The Tower Of Joy On Game Of Thrones?

Bran Stark will return to Game of Thrones in tonight's episode, "Home." Bran possesses rare gift that allows him to peer into the past, present, and future of Westeros. The trailers for Game of Thrones Season 6 hinted that one major moment that Bran made see, and thus reveal to audiences, is the Raid on the Tower of Joy, a key moment in Game of Thrones history that has yet to be revealed in full in George R.R. Martin's novels. In anticipation of Bran's return, we thought we'd delve into what the Tower of Joy is, and why the raid is such a talked about moment among fans.

WARNING: POTENTIAL SPOILERS FOLLOW

The Tower of Joy was secluded in the Red Mountains of Dorne. This was where Ned Stark found his sister, Lyanna Stark, at the end of Robert's Rebellion. It was the kidnapping of Lyanna by Rhaegar Targaryen that sparked Robert's Rebellion to begin with, and it was here that the Rebellion would end.

Stark came to the Tower with six companions: Howland Reed (father of Jojen and Meera Reed), Lord Willam Dustin, Ethan Glover, Martyn Cassel, Theo Wull, and Ser Mark Ryswell. When they arrived, they found the castle defended by three members of the Kingsguard: Lord Commander Gerold Hightower, Ser Arthur Dayne, and Ser Oswell Whent. Stark and Reed were the only survivors of the ensuing battle.

When the battle was over, Ned and his friend went inside the Tower. There they found Lyanna on her deathbed. With her final words, Lyanna had her brother swear a promise to her. Afterwards, Ned had the tower pulled down and used the stones from the tower to build eight cairns, one for each of the fallen combatants.

The key here is Ned's promise, the details of which haven't been revealed book readers or television viewers. Within the world of the Seven Kingdoms, following the execution of Ned Stark, the only person alive who knows what Ned promised is Howland Reed, and he's become a recluse who rarely leaves his floating island castle.

But in the real world, fans have speculated. A lot. The most prominent theory? That Lyanna made Ned promise to protect her son, whom the world knows a Ned's bastard, Jon Snow.

This fan theory – commonly referred to in code as "R + L = J" for "Rhaegar + Lyanna = Jon" – posits that Eddard Stark doesn't have a bastard son, but that he only made that claim to protect his nephew, who is all that remains of his beloved sister. If this fan theory turns out to be true then it will have huge ramifications on the world of Game of Thrones. Not only would Jon be legitimized, but he would also be a Targaryen, blood of the dragon, nephew of Daenerys, candidate to be one of the three vaguely prophesized "heads of the dragon," and in line to become heir to the Iron Throne.

So why the need for secrecy? As mentioned, Robert's Rebellion began when Rhaegar kidnapped Lyanna, who was betrothed to Robert Baratheon (although other fan theories question if this is an example of history being written by the victors, and if this "kidnapping" was actually an eloping). Robert, a passionate man with a thunderous temper, was so infuriated that he led an open revolt against the Iron Throne, with the help of allies Eddard Stark, Jon Arryn, and the might of their respective Houses.

But Robert and Eddard had a fierce disagreement about how the war was ending. The two friends rode together to sack King's Landing. The sack was successful, largely due to the Lannisters switching sides at the last minute. Jaime killed King Aerys, while Gregor "The Mountain" Clegane and his men went to Maegor's Holdfast, where Rhaegar's wife, Elia Martell, and children were. The mountain brutally murdered the infant heir, Aegon, in front of Elia, then raped and murdered her while his men brutally murdered her daughter, Rhaenys.

The bodies of Elia, Aegon, and Rhaenys were presented by the Lannisters to Robert as a show of fealty towards their new king. Robert was pleased, but Ned was disgusted by the murder of children and found the whole thing to be barbaric and unnecessary. He argued with Robert about it, which is why Robert did not join Ned when he left to finish the war.

Fans believe that, when presented with Jon, Ned Stark saw Lyanna in him but feared that Robert would only see Rhaegar and demand the child murdered like the rest of the Targaryens. So it was that Eddard Stark, considered one of the most honorable men in Westeros, sacrificed his honor to make sure that King Robert would never learn that Jon had so much of a drop of Targaryen blood running through his veins.

When Jon and Ned last spoke – as Ned rode off to King's Landing and Jon to the Wall to join the Night's Watch – Ned promised that the next time he and Jon spoke Ned would tell Jon about his mother. Fans believe that Ned planned to tell Jon the truth about his Targaryen heritage after Jon said his oath and officially took the black, believing that once Jon had forsaken name, title, and lands he would no longer be a threat to Robert's rule. After all, Aemon Targaryen had been serving as maester to the watch for years. That conversation never happened though. Ned died in King's Landing, leaving Howland Reed as the only person who knows if this theory is true.

But there are other ways, which brings us back to Bran Stark. Could bran finally solve the mystery of Jon Snow's parentage for good?

Game of Thrones airs Sundays at 9 p.m. ET on HBO.