Archaeologists working in Oslo report that evidence from a 2023 excavation is prompting a reassessment of the city’s early development.
A structure long interpreted as the remains of an early medieval fortification is now being reclassified as a Viking Age boat grave, suggesting activity at the site several centuries prior to Oslo’s conventional founding date.
The site lies beneath the medieval royal estate, historically linked to Harald Hardrada. He is often credited with establishing Oslo around 1048, and earlier interpretations of the mound beneath the complex leaned heavily on that timeline. Archaeologists believed it was part of a motte-and-bailey structure—an earthen mound with defensive features typical of early castles. That reading now looks less convincing.
Researchers from the Norwegian Institute for Cultural Heritage Research revisited both the site and older excavation records. They found several inconsistencies. The mound is smaller than expected for a castle of that type, and the surrounding ditch is shallow. Comparable fortifications do not appear in Scandinavia until later, which raises doubts about placing one in Oslo in the mid-11th century.
The dating itself also comes into question. A coin hoard found near the top of the mound had been used as key evidence. But closer examination shows the coins were placed into an already existing feature. That detail suggests the mound predates the deposit.
The shift in interpretation began with a large number of iron rivets uncovered during the 2023 dig. Archaeologists recovered 717 rivets and fragments from layers around the mound. These were not general-purpose fasteners but the kind used in clinker-built boats, a construction method common in the Viking Age.
When earlier finds from the 1960s are included—many of which were never fully analyzed—the total rises to more than 1,100 rivets. They are concentrated within a relatively small area, which makes it unlikely they came from scattered activity over time.
Michael Derrick, an archaeologist involved in the project, said the volume and distribution point to a single explanation. “It’s difficult to see these as anything other than the remains of a vessel,” he said.
The condition of the rivets supports that view. They do not show signs of having been removed, as would be expected if a boat had been dismantled or repaired. There is also little evidence of metalworking debris nearby. In medieval Oslo, wooden structures were typically assembled without iron nails, relying instead on wooden joints.
Taken together, the evidence suggests that the rivets came from a boat deliberately placed at the site.
To assess the finds, Derrick consulted Knut Paasche, a specialist in Viking ship construction. Paasche concluded that the rivets belonged to at least one vessel. Differences in size among them could indicate more than one boat, a pattern seen in other high-status Viking burials.
Radiocarbon dating places the mound in the late Viking Age, likely between the late 9th and early 10th centuries. No human remains have survived, but the lack of cremation traces points toward a burial in which the deceased was placed in a boat and covered by earth.
The location fits that interpretation. During the Viking Age, the area lay close to the shoreline of the Oslo Fjord. A mound in that position would have been clearly visible from the water, marking presence and control in the landscape.
Over time, the site changed. The mound appears to have been disturbed, first in the Viking period and later more extensively. By the 11th century, a wooden palisade stood on the spot. In the 13th century, a stone royal complex was built over it.
Researchers think this reuse follows a pattern seen elsewhere in Scandinavia. Older monuments were often incorporated into new structures, sometimes to reinforce authority by linking it to the past. The coins placed in the mound may reflect such a transition, from burial site to a place tied to royal activity.
The findings have wider implications. If the mound predates Harald Hardrada, then the area was already in use long before the city’s supposed founding. Other excavations in the region have uncovered settlement traces going back to the 7th, 8th, and 9th centuries.
That points to a different picture of Oslo’s early history. Instead of a city established at a specific moment, it appears to have developed gradually, building on an existing landscape of farms, routes, and local power.
The remains beneath the royal site do not just add a new detail. They suggest that Oslo’s origins run deeper than previously assumed, extending back into the Viking Age and possibly earlier.
Header Image Credit : Sara Langvik Derrick
Sources : Norwegian Institute for Cultural Heritage Research
