What lies hidden inside Grønhaug on Karmøy, on the western coast of Norway? Archaeologists opened the burial mound last week.
"The mound may have been somewhat forgotten," Marie Ødegaard tells Science Norway. She is an archaeologist at the Univeristy of Stavanger's Museum of Archaeology.
She is leading the excavation together with Håkon Reiersen from the same university.
Grønhaug is located on Karmøy, among a row of several large burial mounds dating from a wide range of periods. Some are from the Bronze Age.
Ødegaard says the archaeologists have already uncovered something beneath the Viking grave.
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Investigated in 1902
Inside this mound are the remains of a Viking ship. It may have been around 15 metres long, and the mound was first investigated by archaeologist Haakon Schetelig in 1902.
He confirmed that a ship was buried here.
Parts of the ship’s bottom and hull are probably still preserved inside the mound. During the 1902 excavation, archaeologists removed loose pieces of the ship’s planking from around the oar holes, which were well preserved. They brought them to Bergen, Ødegaard explains.
"Most of it was probably left in place because the wood was soft," she says.
The mound has not been opened since then, according to the Norwegian Directorate for Cultural Heritage, which commissioned the excavation in collaboration with Rogaland County Municipality.
Haakon Schetelig's mapping of the trench and the ship from 1902. The archaeologists have opened roughly the same trench into the mound.(Image: University Museum of Bergen / CC BY)
The archaeologists have now opened a trench into the mound to examine the conditions there and determine how well objects are preserved inside the mound.
The trench is roughly the same one that Haakon Schetelig opened in 1902, with a small extension. This is a limited excavation, meaning that the entire mound is not being opened.
"We have found one or two rivets, probably from the ship," says Ødegaard.
Remains of rivets from the ship.(Photo: Jan Magnus Weiberg-Aurdal, Norwegian Directorate for Cultural Heritage)
Little left of the ship
This ship is very badly deteriorated, so little remains of the ship itself.
"But we have found timber from the grave that Schetelig discarded when he excavated here," Ødegaard tells Science Norway.
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This timber is probably not part of the ship itself, as it appears to be pine, according to the archaeologist.
Viking ships were usually built from oak, although parts such as a superstructure could have been made from pine.
"It may have been part of a roof or other objects aboard the ship," she says.
But these pieces of wood were very well preserved, which was one of the reasons for investigating the mound.
The grave has been looted
One question is whether objects and artefacts inside the mound are deteriorating rapidly. But preliminary investigations show that preservation conditions inside the mound are very good, Ødegaard explains.
Archaeologists have now taken the opportunity to examine a layer of birch bark found inside the mound.
"Previously, it was thought that the birch bark was connected to the looting that took place at the end of the 10th century. One possibility was that it had been laid down so people could walk through the mound without getting their feet wet. Another was that it had some ritual purpose, perhaps to avoid disturbing those believed to dwell within the mound," says Ødegaard.
In other words, ghosts that people believed inhabited these burial mounds.
"Now we're starting to become less certain about what this actually is, and it may instead have been part of the mound's construction," she says.
Archaeologists from the Museum of Archaeology at the University of Stavanger display birch bark and pieces of wood recovered during the excavation.(Photo: Øyvind Nesvåg / Rogaland County Municipality)
This is another example of the preservation conditions being very good. The excavation also produced some surprises, Ødegaard says.
Blueberry plants from the Viking Age?
One of the questions that remains unresolved is what lies beneath Grønhaug.
Was this mound built as a Viking grave? Or is there something else here?
Several other burial mounds in the area are much older than the Viking Age and date back to the Bronze Age.
The archaeologists found evidence of the same here. Beneath Grønhaug are the remains of a Bronze Age grave.
Ødegaard says that they dug down to the old ground surface from the Viking Age. In other words, the surface that was exposed when the ship burial was built.
"It was so well preserved that I could see blueberry plants and heather that were growing there when they built the mound in the Viking Age," she says.
Here you can see heather and blueberry plants inside the mound – straight from the Viking Age.(Photo: Marie Ødegaard)
"The plants even still had leaves on them," she says.
This means that the mound was built over the vegetation during the summer half of the year.
A Viking grave on top of a Bronze Age grave?
"We have now excavated through the mound, and we can confirm that there is probably a Bronze Age mound underneath it," says Ødegaard.
The archaeologists have uncovered a man-made stone cairn beneath the Viking grave, covered by several layers of soil and turf. This has only just been excavated, so more samples need to be taken to establish a more reliable timeline.
Stones were also arranged around the base of this mound, forming what is known as a kerb.
This older mound appears to have been used as a kind of platform for the Viking grave.
Here you can clearly see into the trench that the archaeologists have excavated. At the far end, you can see large stones that are the core of the Bronze Age mound, while the outer stones are part of the kerb. This is a ring of stones around the mound.(Photo: Marie Ødegaard / University of Stavanger)
"Part of the further analysis will involve dating the mound underneath more precisely," says Ødegaard.
Debate over whether the grave dates from the Viking Age
There has been some debate about the dating of the Grønhaug ship itself. Earlier studies suggested that the ship may have dated from around the year 780 and that the burial took place a little over a decade later, according to the Great Norwegian Encyclopedia.
This would place the grave just before the Viking Age.
But newer datings and reviews of both dendrochronological dating and radiocarbon dating indicate that the ship dates from around 864, and that the burial mound may be a few years older than this, according to a recent review in this research article.
This places it well within the Viking Age. The Oseberg Viking ship, for example, dates from the year 820.
The dating has been the subject of considerable debate, according to Ødegaard.
"It's probably become more precise in recent years," she says. "There is still some discussion, and we hope that this investigation will allow us to establish even more precise dating."
