It's the only thing standing between the mysterious, seemingly evil White Walkers and all the characters we've come to know and love.
Fans have spent years speculating how the White Walkers will manage to get past The Wall - perhaps by going underneath it, or by finding a way to destroy it completely.
But as one keen-eyed reddit user noticed, the intro to season seven's premiere suggested there could be a far simpler method.
These two pictures show what some viewers believe to be the crucial clue.
The first, taken from an earlier season, clearly shows water to the east of The Wall. The second, from season seven, shows the water frozen solid.
Look at the water on the right side. Photo / HBO via news.com.au
This is what it looked like in the season seven premiere. Note the ice. Photo / HBO via news.com.au
The suggestion is that instead of going through The Wall, the White Walkers will stroll around it on the ice.
Sounds too easy, doesn't it? Well, it would certainly be an anticlimax. But before you dismiss the idea completely, there is a bit of evidence supporting it.
In last week's episode, Sandor Clegane stared into one of those creepy magical red priest fires and saw a vision: "It's where The Wall meets the sea. There's a castle there. There's a mountain, looks like an arrowhead. The dead are marching past. Thousands of them."
There is indeed a castle where The Wall meets the now frozen sea, called Eastwatch-by-the-Sea.
Earlier in the episode, Jon had sent the wildlings to man that castle, anticipating a potential attack by the White Walkers. So, it seems there will at least be a battle there.
All too easy. Photo / HBO via news.com.au
However, we're actually pretty confident this "just walk around The Wall" theory will be proven wrong, and not only because it would be incredibly disappointing.
We have been told several times that The Wall has been imbued with magic to, as Benjen said last season, "protect men from what lies beyond".
"While it stands, the dead cannot pass," he told Bran.
Surely that magic would prevent the army of the dead from cheating and skirting around The Wall's edge. Otherwise, what would be the point of building a wall at all?
The more dominant and plausible theory is that Bran, who has been "marked" by the White Walkers' leader, tampered with The Wall's magic by passing through it in the last episode - and could ultimately be responsible for bringing it down.
There's only one way to find out - bring on the next episode.
