After months of keeping everything they can about Game of Thrones Season 6 quiet, the insiders are starting to spill.

As we who watched the filming process are *very* aware, the production spent an inordinate amount of time on a field in Northern Ireland over in Saintfield, where a massive battle sequence was filmed. The production, which generally doesn’t stay anywhere very long when it comes to outdoor filming, was parked there for nearly 13 weeks over the course of the late summer and early fall. Now, for the first time, the producers are opening up to Entertainment Weekly about what they were filming. Writer Byran Cogman says:

It’s definitely the biggest action sequence yet. We’ve always wanted to get to a place – story-wise and budget-wise and time-wise and resource-wise – where we would be able to do a proper battle, with one army on one side, one army on another side.

Part of the reason the show has never quite been able to do a proper battle is because of its commitment to not including a lot of CGI in fight scenes (unless, you know, White Walkers are involved.) That means that, in order to film a full-on battle, the producers need the cast, the manpower, and the money for practical effects, which is no small task. Showrunner Dan Weiss discusses this logistical nightmare:

We wondered, ‘Why don’t you see more fully fleshed-out battles in movies and TV?’ Then you get into the nitty-gritty of what it takes to actually shoot these things in a way that isn’t just helter-skelter chaos but actually gives you a sense of battle geography and the ebb and flow, and you realize why.

As those who paid attention to the spoilers knew, Miguel Sapochnik, who is directing episodes 9 and 10, was on hand. Sapochnik directed last season’s “Hardhome,” which was a big part of the reason he was chosen to tackle this episode. Quoth showrunner David Benioff:

Miguel did such a fantastic job with ‘Hardhome’ we thought we should bring him back – this time with horse. Horses are not easy, at all. And certainly in terms of numbers – number of extras, number of stuntmen, number of shooting days – it’s the biggest we’ve done.

EW refuses to give any details on which armies are fighting or what characters are involved, although we have some idea.