Thursday, May 28, 2015

Add this to your to-do list!

Given that a quarter of me hails from Bergen, Norway, and that I had recently read that a Viking settlement had been found near the mouth of the Hudson River, and that Minnesota, my other home, is home to the Vikings, I looked forward to visiting the famous Viking Ship Museum in Roskilde, Denmark, on the Roskilde Fjord, about forty kilometres west of Copenhagen.

I didn't realise what a gem it is.

View onto Roskilde Fjord from inside the museum

Another view onto Roskilde Fjord from inside the museum

A thousand years ago, Roskilde was the capital of Viking Denmark, and continued to be so for several hundred years.  At the time, it was a thriving town with extensive trade connections to all points of the compass.

Its success also brought danger.  Leaders from other parts of the sprawling Danish empire wanted to wrestle control away from Roskilde.  Knowing this, the inhabitants of Roskilde devised a plan to fend off attackers.

To reach Roskilde, an invading fleet would have to sail down the whole length of the Roskilde Fjord – a journey that would take several hours even in the very best conditions.  So Roskilde developed a series of signal fires from the mouth of the fjord.  Should enemy ships be seen, a fire would be lit.  A bit further down the fjord, spotters would see this and set fire to their own pile of wood.  And so on.  It wouldn’t take very long before the alarm would be raised in Roskilde itself, leaving time to muster the defences before the invaders' boats arrived.

To slow the advance of an attacking fleet even more, a barrier was erected in the shortest of the channels heading to Roskilde, near a place called Skuldelev, forcing the boats to take a longer route, which was guarded with a movable barrier.  The Skuldelev barrier comprised five different Viking boats that had been purposefully scuttled and filled with rocks to prevent passage.

They were found in 1962 and are known as Skuldelev 1, 2, 3, 5, and 6.  Originally there were thought to be six ships, but later, researchers concluded that 2 and 4 were from the same ship, subsequently called 2.

And it certainly was one of those discoveries archeologists dream about – five different Viking boats, with much of the timber still intact.

Obviously there were enormous difficulties in recovering the boats – they were under water and had been so for a thousand years, the timber was incredibly delicate and could easily disintegrate if allowed to dry, and there were thousands of pieces lying around that needed to be numbered and classified in three dimensions so the entire scene could be recreated exactly.

The way they proceeded was to build a coffer dam around the boats, slowly drain the water, while at the same time keeping it wet through spraying, then proceed with the recovery.
Once recovered, instead of letting the wood dry out, archeologists sprayed it with a form of large-molecule polyethelene glycol (PEG 4000), which impregnates the wood, allowing it to be displayed in the air.

The coffer dam

Remains of a Viking longboat

Then they studied each of the ships and built frames as accurately as they could to support the wood they had found.  All five of these ships are in the museum.

Skuldelev 1 was a cargo ship about 16 metres long and 5 metres wide, displacing 21 tons.  It is 60% preserved.  Using principles of dendrochronology and the location of tree species, it is pretty certain that it was built in western Norway around 1030 from oak and pine.  A replica, called Ottar was built in 2000/2001.  

Remains of Skuldelev 1

Another view of the remains of Skuldelev 1

Ottar - replica of Skuldelev 1

Skuldelev 2 was an oak-built, sea-going warship, possibly of the skeid type.  It is approximately 30 metres long and 4 metres wide.  It would have had a crew of 70-80 soldiers and would have been very fast, with 60 oars and a large sail of about 110 square metres.  It is thought it was built near Dublin, Ireland, in about 1042, with wood from trees felled in a place called Glendalough.  It is 25% preserved.  The replica was built from 2000 to 2004 and called Havhingsten fra Glendalough (the Sea Stallion from Glendalough).

In 2007, the Sea Stallion, crewed by 65 men and women. returned to Dublin via the Orkneys and Shetlands, then journeyed back to Roskilde around the south of England.  You can see a short video of this epic journey at and a remarkable long video (90 minutes) by the BBC at  I highly recommend watching the longer one.  

Sea Stallion from Glendalough

Sea Stallion from Glendalough on sea trials

Watching these videos and given my propensity for sea sickness, I probably wouldn’t have been a Viking marauder.

Skuldelev 3 was a cargo ship, 14 metres long and 3 metres wide, possibly of the Byrding type.  It is made from oak and was constructed in Denmark.  It would have been ideal for shorter journeys around Denmark.  It was about 75% preserved.  The reproduction was completed in 1984 and called the Roar Ege.

Skuldelev 3 remains

Inside the Skuldelev 3

Skuldelev 3 at sail

Skuldelev 5 was a smaller warship, possibly of the Snekke type.  It was built of Danish oak, ash, and pine, partly by reusing timber from other ships.  It was about 17 metres long, 2.5 metres wide, and had a draught of only 0.6 metres, which made it almost amphibious.  It could move through extremely shallow water and be easily pulled ashore.  It had 13 pairs of oars and carried 30 fighting men.  It was found about 50% preserved.  Two replicas have been built:  the Helge Ask by the museum, and the Sebbe Als  by a private company. 

Skuldelev 5 replica Sebbe Als at sail

Skuldelev 6 was a combined fishing cargo vessel, about 12 metres long, 2.5 metres wide, and 0.5 metres draught.  It was about 70% preserved.  A replica, Kraka Fyr, is on view at the museum.

Kraka Fyr

What made the museum even more fascinating was that the replicas of all of the boats were made using the same tools and techniques as would have been used when the boats were originally built.  The museum is not only a ship museum, but also a ship-making museum, with sections making rope, sails, and so on.

Boat being built Viking style

But wait, there’s more!

All of the Skuldelev boats are displayed in a custom-built museum on the shores of the Roskilde Fjord.  It is truly stunning.

In 1997, construction started on a harbour next to the museum for the various replicas and other traditionally-built boats.  (Perhaps we should suggest that one be named the Rra Kubu.)  During the construction, nine other Viking boats were found, including the largest longboat ever found – it would have been 37 metres long (about 125 feet) – twice the length of Columbus’s Santa Maria.  Historians speculate that due to its immense size it could have been built for Cnut the Great (commonly known as King Canute).

Keel of longest longboat

The preservation of the timbers from these boats has taken years and employed more advanced techniques than those used on the Skuldelev boats.  Here’s a brief description of how they did it, taken from the informative Donsmaps website (
For the Roskilde ships, PEG 2000, a lower molecular weight form of the preserving agent was used, which penetrated the wood better. It acted as a stabilising agent, and acts as a cryoprotector during the freezing stage, when the wood is dried using a vacuum freeze drying process. The concentration was increased from 10% to 40% over a period of three years or more. The final impregnation was at 95% at 60° C or at 50% at 20° C depending on the degradation pattern. The drying period depended on the thickness of the objects and lasted from a few months to more than half a year. 

The Danish team of conservators and technicians, led by Kristiane Straetkvern, have been responsible for the conservation and analysis of the surviving timbers of Roskilde 6 (approx. 20% survives of the original ship).

Restoring the great longboat
 The pieces need to be put into moulds in order to obtain the correct shape. At the time of excavation, complete and thorough 3D measurements of all the pieces was undertaken, making this possible. The moulds and wood were placed in the vacuum freeze-dryer and frozen to about -30° C. The ice is then sublimed by vacuum freeze-drying, which takes from 4 to 6 months, depending on the thickness of the objects. 
After conservation, the planks were dry, but not shaped to fit into the reconstructed ship. Moulds for each plank were prepared, and the dry, full PEG impregnated plank was placed on the mould and heated to 60° C in a humid chamber for several hours until the PEG melted and the wood became flexible. While still warm, the plank in the mould was given the correct curvature, fragments were connected with toothpicks or thin wooden and metal sticks and the wood left to cool and solidify. The plank was lifted to the supporting frame and mounted. 

Walking around the dock and seeing the replicas was an amazing experience.  I was totally gobsmacked by the museum and what they do.

Put it on your to-do list.

Stan – Thursday

Acknowledgements:  I have used materials and photos from Don’s Maps ( and from the English version of the museum website ( 

The museum also has a diorama of a hypothetical raid on Roskilde by a Norwegian Viking fleet.  It was in anticipation of such a raid that the barriers at Skuldelev were put in place.  The diorama is replicated on the Don’s Maps Viking website and very much worth reading.


  1. Seeing as how I was conceived in Bergen, live in Minnesota and read this blog I must get to Denmark and Roskilde. I've only been to Denmark once and missed it. Next time, I guess. If you ever get up to the North Shore I'll buy you a coffee.

  2. Jono, I'll take you up on that - am working on a novella set in northern MN!

  3. Stan, On my to-do list for immediately after I write this comment is to pass a link to this blog to a Viking friend--son of a Norwegian-American shipbuilder. AND to my son-in-law who shares your fractional heritage: one-fourth Bergen. My grandchildren are therefore one-eigth Bergen and have cousins there who have visited them here in NYC. They have all been to Denmark and Iceland, but not to Norway yet. They will put this museum on their list for their next trip to the north country, I am sure.

  4. Magnificent, my next destination!

  5. How interesting to see your take on one of my "local" museums :-) Reminds me to go there again this summer. It is a beatiful place, and very informative. Recently the museum was flooded and it sounds like they have bounced back with flying colours