The size of this longhouse suggests powerful rulers existed in Norway long before the Viking Age

Two years ago, archaeologists excavated a field at Sem in Eastern Norway. Earlier this year, the results came in.

They found a massive longhouse from the 3rd century – much larger than anything ever discovered from that period.

The longhouse was 16 metres wide and would have accommodated at least two of the neighbouring houses that stand there today. A modern, standard prefabricated house is eight meters wide.

But how long was the 1,800-year-old house?

"That's how unique it is"

The archaeologists do not know, because they encountered a road. They did not have permission to dig there, nor on the other side of the road, which is also a field, but with a different owner.

The house continues under the road and onto the other field. 

What they have found so far has excited the archaeologists. The usually reserved experts aren't holding back when describing what the discovery might mean.

"We have to look far beyond national borders to find something similar," says Jes Martens. 

He is an associate professor at the University of Oslo's Museum of Cultural History, and led the excavation at Sem. 

Martens has studied finds from the area north of the Roman Empire, known as Germania, dating back to around the year 0. This region includes what is now northern Europe, above Hungary and France.

"I haven't found anything that corresponds to the house we have now excavated. That's how unique it is," he tells sciencenorway.no.

Before Norway existed

The nation of Norway did not exist in the 200s. The kingdom was formed under Harald Fairhair in 872.

"We have to view present-day southern Norway and Sweden's west coast as one," says Martens.

No one knows what the people in the 3rd century called themselves or how they were organised. Were there many small kingdoms? Were there chieftains with control over an area?

"The common perception has been that there were petty kings with power over a fjord or a smaller area. The discovery at Sem suggests that someone here held power over something much larger," says Martens. 

The Danish online newspaper videnskab.dk asked two archaeologists, who were not involved in the Sem excavation, for their opinions: 

"Major discoveries like this one at Sem challenge established knowledge," says Thomas Grane, archaeologist at the National Museum of Denmark.

"The longhouse is a good sign of centralisation in Norway. When you find something unusual, you also think its use was unusual. That the building was used by someone with special power," says Xenia Pauli Jensen, senior researcher and archaeologist at Moesgaard Museum.

Martens believes they have uncovered a power centre: 

"There's no doubt that the man who sat in Hokksund around the year 200 had the power to rule a large area, perhaps all of southern Norway. People must have listened to him, because he could equip an entire army to march down to Denmark."

A power centre through the centuries

There is much to suggest that Sem and Hokksund have been a centre of power for a long time.

A large house or farm stood there from around 1350, according to lokalhistoriewiki.no (link in Norwegian). In 1602, Christian IV, king of Denmark and Norway, took over the property. A few years later, he added an impressive extension known as the King's House. 

The Hokksund area might also have been a centre of power during the Viking Age. At that time, the Drammen Fjord was up to six metres higher than it is today. That made travel by boat from Sem to Hokksund easy. 

In the neighbouring municipality of Modum, many finds related to iron production have been made. The trade in iron may have been controlled from Sem.

The largest gold treasure in the Nordic countries was found at Hoen Farm, just a few kilometres from Sem. Archaeologists have also uncovered a silver treasure, 20 graves, and 13 individual Viking Age artefacts on farms in Eiker. 

"There was a significant concentration of power in this area during the Viking Age," says Martens.

Gained wealth through the Roman Empire

It now appears that Sem was powerful long before the Viking Age.

Locals may have travelled south as mercenaries to the Roman Empire, where there were constant wars. 

When they finished their service as soldiers, they returned home with weapons and other goods they had bought, earned, or received as gifts or awards.

"Maybe the chieftain at Sem brought back extra weapons and valuables so he could establish himself when he returned home," says Martens.

The returning warrior might have sold luxury Roman goods or given them away to forge alliances. He may have invested in a private army and taken control of iron production.

"Locals may have had to pay him for protection in order to produce iron safely. The export of iron may have gone through his channels. After all, he had contacts to the south," he says. 

There was also local production of weapons, including both swords and spears.

"It doesn't seem like weapons were a problem for them," says Martens.

Sem was ideally located for building power and wealth, given that the fjord reached all the way to Hokksund.

"In southern Scandinavia, it was common to establish towns deep inland but at the end of a fjord. That way, they were protected from surprise attacks. It was the same with Sem," he says.

"Absolutely mind-blowing"

Frans-Arne Stylegar is an archaeologist and cultural heritage specialist at Multiconsult. He has not taken part in the excavations at Sem, but he has followed the work and the results.

He thinks it is a bit early to rewrite the history books based on the discovery of the longhouse at Sem.

"But there are finds in Eiker that have been difficult to explain. Maybe archaeologists are now on the trail of the context they fit into," Stylegar tells sciencenorway.no. 

The Solberg vase is one of these finds. It is dated to around the year 70 and was made in Egypt or by Egyptian glass artists working in Rome. It has long been a mystery how the vase ended up in a bog in Øvre Eiker.

"This Roman vase is incredibly strange. We have nothing else like it in Norway or Scandinavia," he says. 

The Hoen treasure is another find. The oldest coin is from the Roman Empire and dated to around the year 360, while the newest are Arabic and from the 9th century.

"The vase and the treasure are completely unique. So is the longhouse at Sem. Its dimensions are absolutely mind-blowing," he says. 

Stylegar sees the longhouse as a key piece that helps connect the dots for the region.

"It's clear that powerful people have resided at Sem," he says.

Connected to weapons in Denmark

Jes Martens links the house at Sem to archaeological finds in Jutland, Denmark.

Like the Illerup find: In what was once a lake, which later turned into a bog, a large number of artefacts and weapons were found. 

"Tens of thousands of weapons have been found in Jutland. Many of the weapons are from the same period as the house at Sem, and they have been traced to sourthern Norway, among other places," says Martens.

Who had the power and resources to gather an army of several thousand soldiers to attack Jutland?

"Now we might have an answer. It could have been the king at Sem," says Martens.

He shows a map. The warriors who attacked Jutland came from the blue area. The red dots mark finds of weapons from southern Norway and Sweden.

Wanted to conquer Denmark

"From the weapons, we can tell that the army leaders were from the top tier of society, with incredibly elaborate equipment," says Martens.

The weapons cannot be pinpointed to a specific location, like Sem, but they were crafted and decorated according to northern traditions. The soldiers had combs made from moose antlers, which existed in the north but not in Denmark. They also had fire-starting kits with flint and steel – the stones originated from the north.

So many weapons and pieces of equipment were found that Martens believes it looks more like an attempt to conquer Jutland than just a raid.

But the army from the north must have lost the battle, as they were stripped of their weapons and gear.

"When they defeated an enemy, they destroyed their weapons so they couldn't be used again. Everything was burned and thrown into bogs as an offering to the god of war," he explains.

Frans-Arne Stylegar is not as certain that an army organised by a powerful man in Hokksund marched towards Jutland.

"There's an ongoing debate about where all the weapons at Illerup came from. But weapon types have been found that are very common in Norway, especially in inner Eastern Norway regions like Hedmark, Oppland, and Buskerud," says Stylegar.

Where are the boats?

One mystery remains: Even if they marched south through Sweden, they would have needed boats to cross over to Jutland.

Boats from earlier periods, around 400 BCE, have been found. One of these has been reconstructed. Martens has sailed with it.

"It was an oversized canoe with room for 24 people. When we all paddled, we gained good speed. The boat glided like a dream and was perfect for landing. There was also plenty of space for weapons and cargo," says Martens, adding:

"Even in the Stone Age they crossed the Skagerrak. We just haven't found their seafaring boats yet. They might be at the bottom of the sea."

Still, there is one thing missing along the Drammen Fjord, according to Stylegar.

"There are hundreds of foundations from massive boathouses for longships from Roman times, but they're located at Lindesnes and further up along the west coast. There are clear signs that someone had a large war fleet there," he says. 

No such traces of ship traffic have been found in the Drammen Fjord.

"There may have been such boathouses there too, but none have been found," he says. 

Did some come from the south?

There is an alternative story to the one about soldiers returning home and becoming powerful men at Sem and other places in Norway. It is presented in a new book by Professor Dagfinn Skre at the Museum of Cultural History.

There were constant wars in the Roman Empire. There were also bands of mercenaries. Perhaps they travelled north. 

Frans-Arne Stylegar envisions that this might be how it happened.

"It may not have been people who went out to earn riches, but rather someone who came from the south," says Stylegar, adding:

"If there was a period of peace, a group of warriors led by a chieftain might have travelled north to find new hunting grounds. There was land available without strong local chieftains. That gave them the opportunity to establish a base."

That could explain why areas in Norway with many valuable finds from the Late Roman Iron Age show up, even though little has been found there from earlier times. 

Such warriors may have been based at Sem and other places in Eastern Norway.

"That might account for both the numerous weapon graves in the region and the boathouse foundations found elsewhere," he says. 

These warriors may have settled down for a time but also ventured out again. Perhaps it was groups like this that went south to conquer Jutland.

Whether some left and returned, or came and then left again, Stylegar believes that what is happening at Sem is both exciting and promising.

Now it’s up to the county municipality in Buskerud to take things further.

"The historical value is sky-high. Such a large hall from the 200s is incredible. We're very pleased with the results from the excavation at Sem. That gives us strong motivation to continue," says archaeologist Håvard Hoftun from the county municipality.

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Translated by Alette Bjordal Gjellesvik

Read the Norwegian version of this article on forskning.no

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How old is Norse mythology?

Longhouse and Viking grave likely found in western Norway

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