Swedish King Charles XII transported massive ships overland to attack a Norwegian fortress. Researchers have now uncovered the forgotten route

In December, archaeologists from the Norwegian Institute for Cultural Heritage Research (NIKU) conducted a georadar project at Blomsholm in Sweden. 

The project was initiated as a large-scale test of the newly developed AutoMIRA system. 

According to archaeologist and project manager Erich Nau, Blomsholm was chosen as the test site because of its rich cultural heritage. The area is home to Sweden’s second-largest stone ship, the impressive Grönehög burial mound, several other burial mounds, circular stone settings, and traces of settlement.

“This area provides a unique insight into the landscape of the past. But we didn’t expect to find a hidden historical route. The survey shows clear traces of the Galärvägen road from 1718 and is clearly one of the most exciting discoveries from this survey,” says Nau. 

Blomsholm – a unique cultural landscape

• Blomsholm is recognised as one of Sweden’s most important cultural heritage sites, with several spectacular monuments. 
• The large ship setting from the Roman Iron Age consists of 49 stones and is the second largest in Sweden. 
• Storhaugen Grönehög, dating from the Migration Period, is one of Scandinavia’s largest burial mounds and is strategically located on the old coastline. The burial mounds and dome rings in the area testify to extensive activity in the Iron Age and Viking Age. 

Up to 30-tonne vessels were to be transported overland

In 1718, Swedish King Charles XII ordered 12 large ships to be moved overland between Strömstad and Iddefjorden. The aim was to attack Fredriksten fortress in present-day Norway. The attack was to come from an unexpected direction since the fjord’s inlet from the sea was blocked. 

It was a massive operation that required vessels weighing up to 30 tonnes to be transported overland. 

According to Nau, little was known about this transport route before it was discovered in NIKU’s ground-penetrating radar data. 

Instead of the expected prehistoric remains in the vicinity of the impressive Iron Age stone ship at Blomsholm, the survey revealed traces of Charles XII’s transport route. 

Traces of Galärvegen discovered using ground-penetrating radar

Galärvegen is the name of the route used by King Charles XII and his 800 soldiers to transport 12 large galleys overland from Strömstad to Iddefjorden during the military campaign against Fredriksten fortress on the Norwegian side of the border. 

The transport began on June 26, 1718. It required several months of hard work. 

The heavy vessels were moved using hoists, blocks, horses, and greased logs, over 25 kilometres through challenging terrain. 

Preliminary analyses from the ground-penetrating radar survey have revealed several exciting findings. They show several parallel, linear structures that correspond well with this historic transport route. 

These structures start at the southern boundary of the survey area and can be followed over a length of 160 metres, directly west past the ship setting.

The tracks are particularly evident in the southern section. Researchers interpret these as the remains of logs that were laid along the road to stabilise it in soft areas. 

Here, the parallel tracks have an outer width of approximately 8 metres and an inner width of 3.5 metres. Further north, near the ship setting, only the 3.5-metre-wide structure is visible.

In addition to the traces of Galärvägen, researchers have discovered several structures. Preliminary analyses have identified these as prehistoric burial mounds and traces of settlement.

During Charles XII’s campaign, the area around Blomsholm was used as a field hospital. Several soldiers were buried in the ship setting. 

This makes the data challenging to interpret, as the area has been affected by many different activities over the centuries. 

Roger Nyqvist, who works at Bohusläns Museum, sees these discoveries as a unique opportunity to link historical documents directly to archaeological traces in the landscape: 

“The discovery of Galärvegen gives us a unique opportunity to combine historical sources with modern technology to explore and communicate important parts of our common cultural heritage. NIKU’s georadar survey is a valuable contribution to our understanding of Blomsholm as a complex and dynamic cultural landscape through several time periods."

A revolution for geophysical surveys 

The investigations at Blomsholm marked an important milestone in the development of the AutoMIRA system. This is an autonomous ground-penetrating radar system developed by NIKU in collaboration with the Norwegian company AutoAgri. 

The system is designed to cover large areas quickly and efficiently, with a capacity of up to 5-7 hectares per day. One hectare equals 10,000 square metres.

Nau reports three days of continuous surveys with no major technical issues: 

“We were able to survey a total area of 8.5 hectares in just three days. Although there is a need for some more upgrades in the future, this confirms the robustness of the system.”

This means that from the next field season, NIKU will be able to cover larger areas than before. In a short time, they can collect high-resolution ground-penetrating radar data. According to Nau, the autonomous system, combined with the latest generation of radar technology (MIRA HDR, GuidelineGeo), will significantly increase both the capacity and accuracy of the data.

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