On last Sunday's episode of Game of Thrones, appropriately named "The Climb," we saw Jon Snow and the Wildlings scale the Wall, a 700-foot vertical ice barrier that separates the continent of Westeros from the frozen lands to the north (and the Wildlings and White Walkers that live there). In a dramatic climbing sequence, Wildlings roped together in groups of four scaled the sheer face with ice axes in hand, facing several near-death moments as falling ice sent many of them tumbling.

So how realistic was this scene, from the perspective of an experienced ice climber? I decided to find out with the help of Katie Mills, a Game of Thrones fan who also has eight years of experience mountaineering in the Pacific Northwest and lead climbing waterfall ice in Montana and Colorado.

First question: Why were the Wildlings climbing simultaneously while tied together by the same rope? If one climber falls, wouldn't that pull everyone else off the Wall?

"This is a common technique known as a running belay or simul-climbing, where the team climbs at the same time with protection like ice screws placed in between team members," said Mills. The catch, if you will, is that running belays are only appropriate on low angle ice or snow, where the friction of the rope against the terrain makes it easier for a climber to arrest their fall. A running belay should only be used where falls are unlikely, not for the sort of vertical climbing that the Wildlings attempt where the impact of falls is much more massive and almost certain to pull off other climbers.

"Nobody would ever running belay a vertical climb," said Mills. "You'd approach it the standard way, with one person leading, the other belaying from a stationary position, and then the leader building an anchor at the top and bringing the other people up."

While we don't see the Wildlings using modern ice climbing devices like ice screws or metal pickets placed in the snow during their running belay, we do see them pounding curved hooks into the ice. When Jon–the last member of the party–falls after being hit by ice, one hook pops out but the second one holds, and ostensibly "catches" the rope.

But since we see the rope moving smoothly through the hook, how would it stop Jon's fall?

Short answer: It wouldn't. Mills suggested that the hooks might be a medieval reimagining of the carabiner, and similarly would only be helpful if everyone fell and it caught the rope from a position above all the climbers. If anyone is above Jon, they're the ones presumably catching him as they hold on to the Wall–an unlikely proposition given the forces exerted by this kind of drop, which would be many times Jon's body weight.

What would be the more likely outcome? "Jon would yank the person above him off, who would in turn yank the next person off, and then the leader off, and they'd all be dangling from the ice hook with the rope taut." (Inexplicably, right after Jon falls, the rope appears to be slack above him.)

Image: HBO You know nothing about peak forces, Jon Snow. Image: HBO

Similarly, when Tormund embeds his axe in the ice and catches the three climbers in his team during the icefall–and when Jon does the same moments later to save Ygritte–their axes might stay lodged in the Wall, but Mills says the climbers would almost certainly lose their grip on them given the massive force of the falls, which are increased even further by the type of rope they use.

"The ropes we use in modern climbing are dynamic–they stretch, which reduces the force," said Mills. "The ropes [the Wildlings] are using are completely static with no give, so the instantaneous impact force of someone taking a vertical fall would be huge!" Since the force of the fall is concentrated at a single moment, rather than distributed more gradually by rope stretch, there's also a good chance that the impact could snap this type of rope entirely.

Also, either intentionally or unintentionally, Mills says the scene where Orell cuts the rope above Jon and Ygritte is reminiscent of a similar rope-cutting scene in the film Vertical Limit, one of the movies most frequently mocked by climbers for its technical inaccuracies. And it's subject to one of the same nit-picks: When Orell decides to cut the rope and send Jon and Ygritte tumbling, it takes him several moments to saw through it. But with the rope so taut, it would sever almost instantaneously. "You'd barely have to touch it," said Mills.

The Wildlings do use accurate ice climbing gear like ice axes and crampons on their climb, and while the modern tools we see in this episode weren't around in the 15th century ballpark of Game of Thrones, there were more rudimentary versions used by climbers of earlier eras. A form of crampons–ice climbing shoes with spikes–dates back to the 1500s, when Alpine shepherds attached spikes made from horseshoes to their boots. (Mills notes that the Game of Thrones propmasters are using modern Black Diamond crampons adapted to look older.) Similarly, while the sort of ice axes that Tormund and company use are too advanced, they were preceded by an alpine tool called an alpenstock, a longer wooden pole with a spiked tip that also dates back to the 1500s.

Of course, the most dramatic moment in the Wall-climbing scene involves the massive sheet of ice that shears off because of a crack created by Ygritte's axe. How likely is this sort of rippling crack and catastrophic icefall?

Given that the Wall is made of solid ice, not very likely. "While hanging ice curtains or pillars get horizontal cracks and fail catastrophically from people swinging their picks into them, it is near impossible that the ice would crack catastrophically like that if it is a solid block," said Mills. "If solid hunks of ice could crack catastrophically like that, we would not ice climb because the sport would be too dangerous!"

If the Wildlings get a hold of the Horn of Winter, however, then all bets are off.