People were able to cross the open sea from Norway to Denmark 4,000 years ago
For the first time, a team of researchers is uncovering how this was possible.
Large boats like this may have been used for the journey across the North Sea thousands of years ago.(Photo: Lennart Larsen / National Museum of Denmark / CC BY 4.0)
Seafaring during the Stone Age and Bronze Age was much more advanced than we believed just a few years ago.
Especially in Norway and the Nordic countries.
These large vessels may have carried crews of several dozen people. They were far more sophisticated than simple hollowed-out logs.
As early as 4,300 years ago
"Our study indicates that crossings directly over the North Sea between Denmark and Norway likely occurred regularly as early as 4,300 years ago," says Knut Ivar Austvoll, associate professor at the University of Oslo.
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These boats were neither sailed nor rowed.
Seafarers at the time paddled their vessels forward.
"Especially in Norwegian archaeology, we have long agreed that there must have been a fair amount of contact across the North Sea, between Southern Norway and Northern Jutland, at this time. Much of what we archaeologists find in both places is so similar," Austvoll points out.
It concerns metal objects, burial customs, and house construction.
Thousands of years ago, people may have travelled from Norway all the way to the Mediterranean in vessels possibly as large as Viking ships. At Hornnes, you can see an entire armada of 17 Bronze Age ships advancing southward along what was once a rocky shoreline. The markings suggest the ships had large crews, and several are shown with rudders at the stern.(Photo: Museum of Cultural History)
A team of researchers, led by the University of Gothenburg and including Knut Ivar Austvoll as the only Norwegian member, has now compiled statistical data and created models to better understand seafaring between 3,000 and 4,000 years ago.
Their work offers new insight into how people crossed seas during the Stone Age and Bronze Age.
Travelling directly across the North Sea from Jutland to Lista in Southern Norway is a much shorter route than travelling along the coastline of Sweden and Norway.(Image: Bengtsson et al., 2025)
They now also know which routes were most likely taken across the North Sea, Skagerrak, and Kattegat.
The crossing from northwestern Jutland to Lista in Southern Norway spans about 110 kilometres of open sea.
If you instead choose to paddle along the coast – first from Jutland over to Bohuslän, then up to the outer Oslo Fjord and onward down the coast along Vestfold, Telemark, and Southern Norway – the journey stretches to a total of 700 kilometres.
A risky journey across the North Sea
"Although the direct crossing of the North Sea must have been dangerous, it was likely the preferred route for many during the summer," says Austvoll.
This route was by far the most efficient for early Norwegians seeking to trade metals and other valuable goods with people further south in Europe.
"It’s kind of like saying the ferry between Kristiansand and Hirtshals started running 4,000 years ago and has been operating ever since," jokes researcher Flemming Kaul from the National Museum in Copenhagen, in an interview with Danish outlet Videnskab.dk about the new study.
Kaul took part in the first voyages with a replica of the Danish Hjortspring boat in 1999 – a vessel you can read more about further down.
A hundred years ago, it was still common knowledge among people in northwestern Jutland that if you planned to reach Norway in a small boat, you should first sail a bit south along the coast before heading out to sea, Kaul explains – just as the map about illustrates.
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That way, you could follow the ocean current northward.
But it's definitely better to have this modelled accurately, Kaul tells Videnskab.dk. He finds the study very exciting.
Norwegians wanted bronze
In the Late Stone Age, early Norwegians travelled to Denmark to collect flint for making tools.
"A little later, it may have become even more crucial for people in the north to set out across the North Sea in vessels to obtain bronze," says Knut Ivar Austvoll.
During the Bronze Age – between 2,500 and 3,700 years ago – boats were central to a trade network that may have stretched from Northern Norway all the way to the Mediterranean.
In Europe, seafarers could paddle their vessels along rivers or coastlines. Only the English Channel had to be crossed.
But the stretch of open sea from Southern Norway to Jutland was more than three times as long as the crossing over the English Channel.
The closest we come to a preserved ship from the Bronze Age is the nearly 2,400-year-old Hjortspring boat, which is on display at the National Museum in Copenhagen. It closely resembles the ships seen in Nordic rock carvings. Its planks are joined in a way that closely resembles the modern clinker-built technique used in wooden boat construction.(Photo: National Museum of Denmark)
"We’ve been building on archaeological theories that have existed for years. For the first time, we now have scientific data supporting this daring sea voyage," says Austvoll.
The journey took 16 to 20 hours
The Danish Hjortspring boat – a plank-built vessel dating back 2,400 years – was used in this study as a model for Bronze Age boat types. The boat was found in a bog on the Danish island of Als in 1921. It could hold 20 paddlers and a helmsman.
The researchers developed a simulation tool that combined data on wind, waves, and ocean currents. With this, they concluded that:
Direct sea crossings from Norway to Denmark were likely possible during the summer months.
Open-sea travel required boats capable of handling waves up to two metres high and wind speeds of up to 10 knots, or about 5 metres per second.
A direct crossing between Norway and Denmark 3,000-4,000 years ago could take between 16 and 20 hours. The coastal route via Bohuslän and across the Oslo Fjord could take 12 to 22 days.
It's likely that direct crossings of the North Sea occurred regularly as early as 4,300 years ago.
Advanced maritime knowledge
Knut Ivar Austvoll is an associate professor at the University of Oslo's Department of Archaeology, Conservation and History.(Photo: University of Oslo)
"In our study, we conclude that the shorter, riskier direct sea crossing is the most likely explanation for the strong connections between Southern Norway and Northern Jutland during the Bronze Age," Austvoll tells sciencenorway.no.
He and his fellow researchers believe that such journeys must have required advanced maritime knowledge.
People had to navigate without land in sight.
Was it mostly 'Norwegians' who travelled south?
One question Knut Ivar Austvoll raises is whether it was primarily the 'Danes' who ventured north – or was it the 'Norwegians' who journeyed south?
"People living in Norway had already been closely connected to the sea for several thousand years by the time these sea crossings began more than 4,000 years ago," he says.
Austvoll's hypothesis is that communities in the north had developed a level of maritime expertise that those further south may not have possessed at the time.
"This could have given people in the north during the Late Stone Age and Bronze Age a maritime advantage compared to others in Europe," he says.
Austvoll points out that almost everywhere rock carvings are found in Norway, there are depictions of both large and small vessels. These are strikingly similar to the Danish Hjortspring boat that researchers used as a model in their study.
Rock carvings of ships are found along the entire coast of Norway. Note the dragon heads. One of the greatest hopes among archaeologists is to one day discover one of these ancient ships perfectly preserved on Norwegian soil.(Photo: Hans A. Rosbach / Wikimedia Commons)
Boats built for Norway's coastline
For a long time, researchers believed that people in Stone Age and Bronze Age Norway relied only on dugout canoes – hollowed-out tree trunks – or skin boats to move across the water.
But now we know that plank-built boats – constructed by layering wooden planks and stitching or riveting them together – date back to the Bronze Age, and possibly even earlier.
The planks were first stitched together. Later, they were assembled with wooden or iron rivets.
This technique produced vessels that were lightweight, durable, and flexible – ideal for Norwegian conditions.
Just think of the Viking ships that came 2,000 to 3,000 years later and could sail to Iceland and Greenland. Or the many wooden boats along the Norwegian coast in more recent times that are still built using the same technique.
"Building boats with planks was a major technological breakthrough. Today, we can likely date this technological shift to the Late Stone Age, or the period when the Stone Age was transitioning into the Bronze Age. A time when agriculture had also fully taken root in Norway," says Austvoll.
A Bronze Age boat found in Nordland county
The closest we have come to discovering a plank-built boat from the Bronze Age in Norway is the Haugvik boat.
It was found in Haugvik, along the coast of Nordland county in northern Norway.
The boat may be between 2,800 and 2,400 years old.
The Haugvik boat is about 10 metres long.
Its remains were well preserved in a bog, with the planks fastened together using wooden pegs. The bog find lay exposed to the elements for many years before the plank fragments were finally preserved in 1942.
The Haugvik boat demonstrates that people in Norway were capable of shaping planks as thin as 1.5 to 1.8 centimetres – several thousand years ago. Perhaps as early as 2,000 to 3,000 years before the first Viking ships were built. The hull planks were either lashed together or fastened using wooden pegs.(Photo: Sylvester, 2006)
Did people in Stone Age and Bronze Age Norway use sails?
Most Norwegian maritime historians agree that sails did not arrive in Norway until sometime approaching the Viking Age.
Possibly sometime between the year 200 and 500 CE.
However, sails likely did not become widespread until closer to the 800s, during the Viking era.
Still, could sails have been used on boats in Norway as early as the Stone Age or Bronze Age? In Egypt, people began sailing at least 5,000 years ago.
"When we simulated the use of sails on Bronze Age vessels in our models, we found that they were more efficient than paddling for long-distance travel with cargo. We also have Scandinavian rock carvings that depict ships with features that may resemble sails, something lead author Boel Bengtsson has studied," says Austvoll.
That said, this remains a highly uncertain hypothesis.
