Spoilers abound for those who haven’t seen the Dec. 28 episode of “Vikings.”

“Vikings” began with Ragnar Lothbrok (Travis Fimmel), but it was never just his story. There was shieldmaiden Lagertha, and Ragnar’s brother Rollo, and, later, his sons. Yet Ragnar bound all threads together. And now, as history — or, at least, his story — told us would happen, Ragnar is dead, cast into a snake pit by the vengeance-seeking King Aelle of Northumbria (Ivan Kaye) after being handed over by his friend (and enemy) King Ecbert of Wessex (Linus Roache). “Vikings” showrunner Michael Hirst talked to Variety about putting Ragnar and Fimmel through hell, and what comes next.

When did you tell Travis Fimmel this was coming? Presumably he knew just from the historical nature of the series.

Travis came to the show late because I was very unhappy about the people they were trying to cast. I didn’t want a loud Viking, I wanted an intelligent, quiet, thoughtful Viking, and it took Travis quite a long time to come forward. So actually all he had was the first few scripts and the bible for the first season. Now, at the end of the bible for the first season, Ragnar dies. So as far as Travis knew, this was just a one-season job. But as soon as we saw the potential, the great actors, it became clear that Ragnar was needed for much longer.

You really seemed to put him through hell in those final scenes.

I was there that day. It was extraordinary, for everyone who was there. It was a very memorable scene. There are aspects of Ragnar’s death which do echo the Passion of Christ, which is why, without being gratuitous, it had to be very graphic, partly because it made the death so much more significant. You see through the torture Aelle does on Ragnar that he’s trying to break Ragnar, and Ragnar can’t be broken. It’s a great triumph of the spirit. Just as the Crucifixion is graphic, this must be as well.

There’s also of course that human element to it, which is: a man suffering. And indeed, that was shot in Ireland in the deepest winter. It was bitter and pouring rain, and they’d been in that part of the forest shooting for days. It was a terrible mudbath.

And finally there was the moment where Ragnar is in the cage above the pit. Travis was actually suspended in that cage for hours, and the bottom really did open, and the real Travis fell. Travis is a very laid-back Australian, and when I asked him how he felt about shooting his own death and he said, “I’m not worried about it, mate.” But when the time came, he was deeply invested in it. We spent a long time working on the script. When he was in the cage and screaming out those words, it was really him.

When I saw it I wept, knowing that this was the end of a journey that Ragnar and I and Travis and I had been on. It was a creation of both me and Travis together. It was a very moving day. It carries a huge charge in the show, it really does pay off all the hours we’ve invested in him. We do death very well in “Vikings,” but this was a particularly moving.

It also felt so small, in a way. This wasn’t a big, showy execution. It was a couple dozen people in the woods.

It’s realistic and intimate, and because of that it’s more deeply felt and experienced. If you have special-effects armies around and a heroic death, that is essentially an empty death. It is a lot of sound and fury signifying nothing. You were so up close and personal here. You couldn’t escape it, you couldn’t look away to anything else. The most significant deaths do happen normally in history, it only becomes clear later how significant it was. I wanted it to be as intimate as possible, so we were looking into his eyes.

Who’s going to be hit hardest by his death?

It has a profound effect on Ecbert. They were so close despite being so different — they felt a kinship. I always felt the two prior episodes were part of the death, really, the two-hander with Ragnar and Ecbert.

But of course it hits all the sons. Death motivates the sons, gives them a new purpose in life. It informs what happens next in the major storyline of the show.

I’ve always said this was going to be the story of Ragnar and his sons. Ragnar never goes away. We’ve shot nearly 25 episodes after the death of Ragnar, and we’re following the sons still. But Ragnar never goes away, because his presence is still there, as long as Lagertha and Floki and Bjorn are alive. He lives on through his ambitions for his people, and some of his sons pick up on that. Although he’s dead, like Athelstan, he doesn’t go away. He’s still part of the lives of the people.

This is a saga. This is my saga of Ragnar and his sons. Historically speaking, Ivar and Bjorn did actually become more famous than Ragnar.

How soon do Ivar and the others return for their revenge? Ivar, we know from history, was one of the leaders of the “Great Heathen Army.”

It starts the next episode. This is the reaction of the sons to the death of their father. And Ragnar of course had set it up himself, by taking Ivar with him to England. He’s set up the revenge plot. Bjorn will return. All the sons will be part of what was called the Great Heathen Army.

One of the most striking things about Ragnar, just before his death, is just how much older he looks than when we met him, even though in the real world it’s only been a few years since we first saw Travis as Ragnar.

He’s certainly weathered. He’s got all his experiences written on his face. It was very important to me — there are some shows where people never get old and nothing ever changes. And ‘Vikings’ is about real people and real events. We have people who get older and die. So that process is very important. When I look myself back at that first season, my God, he looks like a young guy! He looks fresh! It’s only been four years. But these are huge changes that he’s gone through. We’ve been on this huge journey with him. It’s all written in his face — and on his head, I suppose.