Game of Thrones Director: George R.R. Martin Liked Last Night’s Episode

Spoilers for the June 8, 2014, episode of Game of Thrones, “The Watchers on the Wall,” follow.

Neil Marshall has become Game of Thrones‘ go-to guy for epic battles: in Season 2, he oversaw Stannis’ assault on King’s Landing for the episode “Blackwater,” and on June 8 fans were treated to his take on the Battle of Castle Black in “The Watchers on the Wall,” reportedly the most expensive episode of GoT yet.

Marshall spoke to TIME about the difficulty of working with computer-generated mammoths, “hammer time” and one very important piece of fan mail.

TIME: Do you pay attention to what people are saying about episodes that you direct?

Marshall: I kind of can’t resist. I think if I directed several episodes I might pay less attention, but coming in to do one episode, there’s quite a bit of focus on it so it’s difficult not to notice.

So, what are you hearing today?

The word seems to be generally very positive. I’m really proud and pleased that everybody liked it. You want to spice it up a little bit but you also want to keep the fans happy. As long as the fans are happy, it’s all good. Actually, the biggest seal of approval was that I got an email from George RR Martin last night. He’d just watched it as well for the first time and he loved it. That’s the best one to get. If George is happy, all right.

Did he say he liked anything in particular?

No, it was kind of brief but he was saying that “Blackwater” was a tough act to follow and he was saying that I’d done a great job with it. That was just amazing, to hear that.

Speaking of, how did this last episode compare to “Blackwater” for you? Which was harder to make?

This one was far more complex in terms of the visual effects and the amount of visual effects. In “Blackwater” we had to deal with the ships, but ships are a lot easier to duplicate and put into the action because they don’t do an awful lot, whereas mammoths are far more complex. I had a lot more prep on this one. With “Blackwater” I came in at the last minute, so I’d only had a week’s prep for the whole episode.

Wow. How long did you spend on this one?

This one, I started work a few months in advance, doing set visits and working with storyboard artists. I finally had like just over three weeks for prep just before we shot it. It was absolutely necessary.

What percentage of what we saw was CG, versus actors and sets?

The mammoth is entirely CG. The giants are real guys in costume and make-up and we simply make them bigger, but they’re 100% real. Other aspects were things like the wall; shots featuring the wall are often matte paintings and things like that. We don’t have a 700-foot ice wall handy.

How big is the Castle Black set in real life?

When you first walk on there it does seem massive and you have a lot of room, but once you start filling it with 80 or so people swinging swords around, it gets busy very quickly. It’s a 360-degree set but it only really works from the inside. It doesn’t really have an outside to it. It has a front gate but otherwise it only exists on the inside.

What’s on the outside?

Scaffolding and supports. It’s not very pretty.

How long did it take to rehearse the combat inside the castle?

That was part of the three weeks, spending a lot of time with the stunt guys, planning and rehearsing individual fight scenes. Alliser Thorne and Tormund, they were one of the standouts, and then of course John and Styr was the other one. They were rehearsing weeks in advance.

And how long did that take to film?

They had the moves very accurately down but the biggest problem with that is exhaustion. How many takes can you get with full energy? But it probably took us 4 or 5 hours to shoot each fight sequence. Maybe more, with John’s fight. That involved some elements, like the guy getting the hammer at the end.

That was quite something.

Hammer time!

I’ve read that you’re a student of military history. How does that play into working on an episode like Watchers on the Wall?

It’s not so much direct references. It’s more strategic things – I look at the castle and it’s like, how would I attack it? Where are its weak points? How are these guys actually going to get over the wall? It’s all very well saying they’re going to climb up something, but then when you see it it’s like, you can’t do that, so how are they going to get up? Part of the problem that we have is that regular bows and arrows can’t shoot 700 feet in the air. The guys on top of the wall are completely safe from regular bows and arrows. Then I had this idea, what if the giants have bows as well? A giant bow is going to be much more powerful and will be like heavy artillery, therefore it could reach the top of the wall, and that puts the guys at the top in danger. I don’t know if it’s so much military history as military strategy.

This was also, surprisingly, one of the more romantic episodes we’ve seen recently. The writers really upped the level of romance between Sam and Gilly, compared to how it’s presented in the books, and John and Ygritte get their first big moment in a while (and their last). How do you balance those two very different tones, action and romance?

It’s just about giving each moment its maximum respect. I treat each of them with similar importance, whether it be Sam’s first kiss with Gilly, which was high romance, trying to film it in such a way to give a sweeping sense to it, or with Ygritte’s death. That was high tragedy and I wanted to capture that as well. You do that moment and then you go do some guys knocking it out of one another, and it’s equally important to give it some momentum or visual impact, whatever’s going to give it the power to keep it engaging. As much as it might seem that you can just put two guys in a shot and have them fight each other, that can become very boring.

What went into the decision to have the episode fade to white, rather than black?

I think it was always in the script. He’s walking out of the door into this white, snowy landscape. That was always the plan.