It was death by a thousand cuts — lots and lots and lots of things to do, and lots of things to keep in mind. A simple but amazingly complicated aspect was the fact that we were lighting with sunlight. That seems totally normal — what could go wrong as long as the sun shines? But what I didn’t realize is the sun rises in the east, and sets in the west. [Laughs.] So the direction you shoot in the morning, and the direction you shoot in the afternoon, are opposite to each other, and we had to completely change the schedule to accommodate where the sun was at any one point. Sometimes we would have to start with the end of a sequence. I didn’t really get that until I was standing in the middle of the field.

Do those kinds of challenges ever end up improving the final result?

At least 50 percent of the time, they make it better. The example I keep coming back to is the sequence where Jon Snow gets crushed by all his fellow troops, and has that dying and rebirthing moment. Which really came as a result of the fact that it rained, and the pitch got completely waterlogged — there was nine inches of mud, and it slowed everything down. So I consulted with David [Benioff] and Dan [Weiss, the creators and showrunners] and said, “I think I can complete the sequence if I can go off script and shoot this idea instead, because it’s more containable and it’s not dependent on the weather.” They said yes, and it ended up being a very personal moment for Jon Snow in the midst of all of that chaos.

What was the single toughest thing you were asked to depict?

Having 3,000 horses running at each other, especially after we discovered that horses cannot touch each other. It’s illegal — it’s a very valid rule about protecting the horses. So the very thing we were trying to do was not allowed. And we only had 70 horses.

What was the solution?

You would have one guy run into the frame, and then the horse rider would pull the horse, which means make the horse fall and lie down on its side. Later we would digitally superimpose another C.G.I. horse and make it seem like it had impacted the live one. Pulling horses down, you can do. It’s about turning their necks in a certain direction, and then having two guys with a rope wrapped around the front two legs — they pull the rope, and then it allows them to fall very painlessly onto a bedded mulch base, so they’re falling into a soft surface. But horses are quite smart, so after a couple of times, they won’t let you.