Legend was almost right. But, the "almost" produced one of the most exciting archaeological finds in recent Danish history. When "Margrethe's ship" was excavated in the early 1960s, the underwater barricade turned out to be not one, but five ships. And they were at least 400 years older than anyone had estimated.
Together, the tens of thousands of fragments that were recovered made up five types of Viking ships (two sizes of trading vessel, two sizes of warship and a cargo boat). Raised from the mud, every single piece was meticulously preserved in preparation for the excruciating jigsaw- puzzle reconstruction to begin. The entire process took a little over seven years, and, almost exactly 30 years ago, the results were put on display at the specially built Viking Ship Museum in Roskilde.
The Museum sits right at the edge of Roskilde Fjord and the ships are displayed against the background of the waterway they were sacrificed to protect. They are beautiful, elegant and strong. But more than that, they embody the very soul of the Viking Age.
"The ship was both their car and their Internet," explains Anne-Christine Larsen, curator of the museum. The Viking ships were the secret weapon of the last millennium, faster and more manoeuvrable than anything Europe had seen before. The boats were so advanced that, in an experimental race, board-for-board replicas of the Roskilde ships proved as quick and as sharp as smaller cargo sailboats from the beginning of the 20th century.
The ships enabled the Vikings to spread out from Scandinavia to raid, trade and settle their way from Newfoundland to Baghdad and from Greenland to Byzantium.
They allowed them to conquer England, seize Paris and establish Viking trading towns overseas, in places such as Dublin. In short, it made them rich and powerful.
"It was a period in Scandinavian history when we were big fellows. A glorious time," says Anne-Christine, excitedly. "It was when Denmark was founded and when cities were created for the first time. It was when we were Christianised."
Despite its importance in history, the Viking Age was left largely unexplored by archaeologists until a few decades ago.
Anne-Christine is one of its investigators and she approaches her period with a passion. "You should work on the periods you find most interesting and can identify with or see yourself in. Being an archaeologist shouldn't mean sitting in dusty offices reading old books. It's being a detective and collecting evidence to tell a story."
As well as studying any written or pictorial sources, collecting such evidence involves working with a crew of experts: linguists to determine possible Viking settlements through place names; scientists to analyse pollen records and determine when and where juniper trees were cut down to make boats; forensic archaeologists to examine grave sites for clues to rituals; craftsmen to build replicas of Viking clothes and tools; and traditional boat builders from other cultures for advice and comparison.
Amateur and professional enthusiasts can both try their hand at building one of those floating marvels - or even take one out for a sail - at the interactive Viking Age workshops on an island that the Museum recently built specifically for this purpose. While excavating the site that had been chosen for the workshops, the remains of nine more ships were discovered - which means current visitors can still see the preservation work being carried out on them at the workshops.
Anne-Christine wants her museum to bridge both the past and the present. "As archaeologists, we have an obligation to inform the public about history and heritage," she explains. "By finding out about your past you can understand your own time. So, by feeling what it was like to build a Viking ship and to sail on one, it brings you closer to the Viking Age." And, after a trip in a Viking boat I can tell you one thing. If they were anything like me, the Vikings spent a lot of their time feeling seasick. Rich and powerful maybe, but definitely queasy.