The sport was brutal and played to the death. Berzerkers are dancing and screaming. Longboats are shallow and stealthy. The Viking Age detail in The Northman is based in history, and writer-director Robert Eggers took pains to get it as close to the real deal as possible.

The Northman is the tale of Prince Amleth who is determined to avenge the murder of his father by his uncle. It is a tale you have heard before, most likely through Shakespeare's version of Hamlet.

Although his films blur the line between reality and magic, Eggers has become known for his intense attention to historic detail with films like The Lighthouse, set in an isolated lighthouse in the 1890s, and The Witch, set on a Puritan family farm in 1630s.

In The Northman, Eggers goes to the Viking Age in the Nordic countries to avoid dumb horned helmets. We asked the three people who worked on the film to explain what they did to dig into the artifacts, literature, and legends that inspired those in the film.

How to build a Viking world 

Ethan Hawke as King Aurvandil War-Raven in "The Northman"

Ethan Hawke rides back into the stronghold as King Aurvandil War-Raven. Credit: Aidan Monaghan

Over decades of bloody revenge plans, The Northman moves through meticulously detailed Nordic locations, with wooden buildings adorned with shields, garments, and carts, inspired by various artefacts and literary sources. In the North Atlantic in A.D. 895, we careen through a stronghold fort, where lies the royal longhouse of King Aurvandil War-Raven and Queen Gudr. We are dragged through a one-shot berzerker attack on a Slav village where families attempt to flee their wooden houses.

Craig Lathrop, the production designer for The Witch, built the farmhouse using techniques and tools from the 17th century. The team pored over 19th-century lighthouse keeper manual and photographs. The scale of The Northman made it necessary for Eggers to reduce the use of traditional building techniques.

In Ireland, timber is very expensive. We are working at a level with such excellent craftsmen that the finishes are as good as in the paint job to make it look realistic. Anything that got close to the camera would be real wood.

The production of the film was advised on by multiple experts. Neil Price has written several books on the subject.

It is too strong a word to describe the fort, and Robert decided what kind of place he wanted it to be. The way in which the trunks of trees are laid along a bank to make a wall is from several sites in Europe. The gantries along the top are kind of conjectural, but we know what they looked like from other sites.

The decorations within Aurvandil's royal hall, which made me audibly gasp when I watched the film, are inspired by the ornately carved Oseberg ship, which was found in 1904 outside.

 The Oseberg ship from around 800 AD, one of the most well preserved Viking ships from the period.

The Oseberg ship dates from around 800 AD. Credit: Noe Falk Nielsen / NurPhoto via Getty Images

The majority of the armor, clothing, and weapons in The Northman are inspired by artifacts found in Viking graves and carvings. Amleth's fateful sword, narrative-wise, actually comes from before the Viking Age. It was based off a few different swords, including the 6th-7th-century Sutton Hoo sword found intact at the famous burial site near the English town of Woodbridge.

It was a palimpsest, every scene is like that.

Ethan Hawke in a helmet.

"There's very few things which are from one particular place, because we have to work with fragments." Credit: Aidan Monaghan

One of the most terrifyingly effective means of interacting with recreated objects was practiced by the cast of The Northman.

The boat was built exactly the way a longship would have been a thousand years ago.

It was easy to row. The Vikings were able to go up shallow rivers and attack where most people didn't expect to be attacked by longships. We had to do it ourselves, we had to practice a lot. Robert would not allow us to have a motor.

Amleth plans his revenge while posing as an enslaved man on a farm owned by his uncle. Price says that it is the most accurate of all the sets in terms of building technique. Even though they were shooting in Northern Ireland, the grass was planted a year before the shoot so it would be the right type of grass.

You just absorb it because Robert doesn't go in for exposition. In the beginning of the film, they are from Aurvandil's hall. The world has come down. The tapestries are too long for his walls because his house is small. They are bunched up in the corners, because he crams them in there.

The Northman has an ancient sport called Knattleikr, which is a hockey-style game, on the farm, and it's a scene in which Amleth is forced to play a violent sport for the pleasure of his masters.

Some historians think that the game was all about who was the last man standing.

The modern viewer likes to experience a multi-sensory experience when watching films. Further pulling us into Amleth's perspective is the fact that Eggers builds visual worlds so carefully detailed that you can almost smell them. That smell is repugnant. The Northman score features lead instruments from the Viking Age, as well as lyres made of horsehair.

For a fictional film like The Northman, accuracy is important.

We all know what the bar is for accuracy. It also cuts down on time, because we know one of the things that this does for the audience is that it hopefully makes it more transportive and immersive, because the atmosphere is an accumulation of details. We can get to more details quicker if we draw from research, but I feel like I can't really do that.

The historical accuracy goes further into the mindset of the vikings with the set decoration or props. For most of the time, it's the Viking man.

To be Amleth, or not to be, that is the question

Alexander Skarsgård as Amleth and Anya Taylor-Joy as Olga, both on horses, in "The Northman."

Alexander Skarsgård as Amleth and Anya Taylor-Joy as Olga Credit: Aidan Monaghan

The elevator pitch for The Northman is essentially Hamlet but Vikings, but the inspiration for Shakespeare's tale actually came from the Nordic character of Amleth. He is a legendary figure, but stories like this always play an important role in anthropology.

The modernity of the Sagas is something that excited me when I started reading it, and the fact that the characters have a lot of different things.

Amleth is obsessed with revenge and the idea of being bound to his fate, having to decide between kindness for your kin and hatred for your enemies.

Amleth has no problems with revenge, unlike Hamlet, says Eggers. In The Northman, he doesn't do that, but when he is pretending to be an enslaved person on the farm, he is a dullard. Sj and I based him on other saga heroes.

"Amleth has no problems with revenge, whereas it's an existential crisis for Shakespeare's Hamlet."

The relationship between the Amleth of the movie and all the Amleths is quite loose according to Price. There are some earlier things, but they are a bit incomplete. The Saga Amleth is much later. Shakespeare is doing his own thing, which is not very close to the Amleth. Robert went back to the source, but also made his own. He wanted to make an Amleth movie that was believable and realistic, one that was also anchored in as much realism as he could give it.

It is difficult to be historically accurate in Eggers films because of the divide between the real and Unreal. When your story is set in a society like that of the Vikings, there is no boundary between the two states of being.

There was no line between the two realities in the Viking age. It was reality for them.

"There was no such thing as an agnostic or atheist Viking. All that stuff was as real as the grass you're standing on."

The character of Amleth, and his belief in fate, ritual, and the presence of Norse gods and spirits, was researched by Skarsg. This was something that was taught from birth, not a belief system.

It was important to understand Amleth's relationship to the spiritual world, the supernatural, because that is a big part of the movie.

It was important to understand that the Vikings believed in the Norns of fate that would weave the fates of each and every man. There was no such thing as an unbeliever. It was as real as the grass you were standing on.

It's a concept that's foreign to us, where we talk a lot about belief systems.

Unleashing the beast within 

Alexander Skarsgård roaring in a bear pelt in "The Northman."

"The beast comes out and he doesn't try to fight it but actually lets it out, which was quite a trip.” Credit: Aidan Monaghan

Ritual is as important to people in the 8th to 11th centuries as breathing. The power of ritual in relation to existence is something that Eggers is familiar with. One scene in The Northman that Price says shows a pretty accurate Viking ritual is when Amleth and his group of berzerkers prepare to invade the Slav village. There is a scholarly split over the specifics of berzerkers, but this kind of ritual was a sort of dance to get yourself in the mood to go into battle.

This scene shows a group of warriors shuffling around around a fire, then descending into howling fury, which will allow them to commit atrocities in the future. It is a prominent ability in Viking lore.

The elite warriors of the time were werewolf and bear warriors.

The warriors were part of a war cult where they would perform a ritual spear dance, and our historians liked the best of the best. Through this ecstatic ceremony, they in their minds, but literally, in their minds, they turn into kind of werebears and werewolves, these beasts on the battlefield that make them basically invincible.

According to Price, rituals like the one seen in The Northman have been represented in pieces of art from the Viking Age and written descriptions from the Byzantine world about people fighting Vikings. He says he is really pleased with that.

Some of the images of men dancing with spears and bear skins on their bodies have strange headdress. It is like a headband with horns. These helmets are not horned. They are not, because men leaping around howling could go wrong.

The transformation part of the berzerker ritual scene was left to the actors.

It was very freeing. I was excited about those scenes, it was like a dance they go into, the berzerkers, in order to awaken. We had to rehearse that part, but then the second part, which was quite unusual, we didn't rehearse at all.

This blurred line between human and animal, between suppressing and unleashing one's inner beast, is the work of Francis Bacon, whose exhibition Man and Beast just finished up at the Royal Academy in London.

I wish I had seen that before I shot the sequence, because it felt like a lot of the paintings by Bacon are about how you hold onto your beast. It was quite a trip when the beast came out and he did not try to fight it.

One of the most violent scenes in the film is the ritual for Amleth.

This level of unleashing the beast comes with some uncomfortable modern associations, and The Northman is an examination of Viking men. There is a cold truth to Viking male violence according to an article written by Price. At the height of the 9th-century raids, Viking armies shattered the political structures of western Europe, with the loss in blood and treasure being immense. There were parallels at home, too, not just in the form of civil warfare between rival kingdoms, but also in domestic violence.

They do terrible things and they are seen to do terrible things, and that is important to Price. I don't want anyone to come out of that scene and want to be a viking.

When you are absorbed in gruesome Viking raids, family drama, and a decades-long quest for revenge, you might not be concerned with the detail in the longhouse. That's the point. You are supposed to arrive in this world without a cheat sheet and try to survive. It is authentic.

The Northman will be showing in cinemas in the UK and the U.S. on April 22.

The brutal one-take battle scene in The Northman got made.