Credit: HBO

Game of Thrones is a notoriously difficult show to make, even when everything is going perfectly. The globe-spanning locations, the sprawling cast and crew, the special effects — the series has similar production values to a big-budget feature film, except it’s 10 hours long. When shooting the upcoming sixth season, the Thrones team was thrown a bonus challenge when there was a rockslide at the show’s Castle Black set.

The Castle Black scenes are filmed in Northern Ireland’s Magheramorne Quarry, where a practical and functional castle set rests at the bottom of a rockface (the rock wall is then dressed as “ice” and extended with special effects to look like The Wall as seen in the photo above). The region also gets heavy rain. Many scenes shot in the quarry are actually filmed during an extremely cold winter downpour, which you don’t see in the show as rain typically doesn’t show up on camera (many nights filming The Battle of Castle Black, for instance, were actually shot during heavy rainfall).

All that rain, however, apparently disrupted the quarry’s “seismic profile,” as experts later euphemistically explained to the Thrones team.

“Once people saw the small pebbles start to come down that turned into slightly larger pebbles, everybody made the group decision to immediately step away from the set,” showrunner Dan Weiss said dryly.

Or as Ser Alliser Thorne actor Owen Teale more dramatically put it: “A piece of rock the size of a London townhouse just fell.”

Nobody was hurt, but since the rockslide happened early during the production year, it created an enormous challenge for executive producer Bernie Caulfield and producer Chris Newman, who map the show’s labyrinthine shooting schedule that plots when every scene is shot many months in advance (which is itself a TV rarity — most dramas can’t tell you exactly what they’re shooting next week, but given the complexity of Thrones and the schedules of its in-demand cast, every element has to be figured out far in advance). “Bernie and Chris already have hardest scheduling job in the film and TV industry, and they had this thrown into the works too, which caused them to drastically reschedule the whole season on the fly,” Weiss said. “But they did it, and we got everything we needed in that quarry after it was seismically shored up and netted and proper protection measures were taken. It actually worked out for the best — some of the stuff we were shooting in that location benefited from the additional prep time the rockslide gave us.”

For more on how the Thrones team pulled off season 6, get the latest issue of Entertainment Weekly which goes behind the scenes in Northern Ireland and Spain, plus profiles six of the show’s female stars. EW has plenty of online Thrones coverage planned, too — exclusive news, cast interviews, recaps, and more (without spoiling any of the significant twists to come). Follow @jameshibberd for ongoing GoT scoop, subscribe to our Thrones email newsletter, and bookmark this page for our latest GoT stories. Thrones returns to HBO on April 24.

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Game of Thrones

HBO's epic fantasy drama based on George R.R. Martin's novel series A Song of Ice and Fire.

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