When the Vikings landed at the holy island of Lindisfarne in 793AD, it marked the beginning of hundreds of years of terrifying raids, which would earn the Norsemen a fearsome reputation as murderers and pillagers throughout Europe.
But the reason why groups took to the seas in the first place continues to divide historians, some blaming over-population in Scandinavia, and others seeing it as a preemptive strike against the seemingly unstoppable march of Christianity.
Now a new theory suggests that the Vikings actually had matters of the heart on their minds.
Dr Mark Collard, Professor of Archaeology at the University of Aberdeen and currently the Canada Research Chair at the Simon Fraser University in British Columbia, Canada, along with colleague Ben Raffield and Neil Price, Professor of Archaeology at Uppsala University , believes that changes in society had led to a desperate shortage of marriage partners.
The growth of polygamy and social inequality in the late Iron Age meant that richer men took many wives, or concubines, causing an inbalance in the male-female sex ratio.
Suddenly young poor men had little chance of securing a wife unless they became rich and well-known quickly, says Prof Collard. And raiding was a shortcut to heroism and treasure, he believes.
“What is clear is that the sex ratio would have been substantially biased and increasing through time, and even small amounts of bias can have a big effect,” he said.
“In a population where just a few powerful older men are able to have multiple concubines you end up with a large number of young single men quite rapidly. Some men would have two to three wives, but the Norse sagas say that some princes had limitless numbers.
“So raiding was away to build up wealth and power. Men could gain a place in society, and the chance for wives if they took part in raids and proved their masculinity and came back wealthy.
“Because polygynous marriage increases male-male competition by creating a pool of unmarried men, it increases risky status-elevating behaviour.”
Surprisingly the idea was first put forward by the Norman historian Dudo of Saint Quentin who argued in his 10th century work, The History of The Normans, that the Viking raids were sparked by an excess of unmarried young men.
Similarly the English antiquarian William Camden in his 1610 work Britannia suggested that the ‘Wikings’ were selected from areas of overpopulation after they “multiply’d themselves to a burdensome community”.
But in recent years the theory has lost support from historians with many believing that raids were a quest for retaliation against Charlemagne’s bloody campaign to force Scandinavian pagans to convert to Christianity – killing those who would not be baptised.
However Prof Collard believes new research into psychology, and other ethnographic studies of tribes, now make the new theory more plausible.
Recent studies found that aggression rises when there is a shift in the male-female sex ratio and where the percentage of unmarried men is greater, the rates of rape, murder, assault, theft and fraud also rise.
New research has also shown that Yanomamo tribes in South America resort to inter-village raiding for polygamous marriages.
Norse sagas such as The Saga of the People of Laxardal and the Saga of Harald suggest that by the time of the raids polygamous behaviour was normal in Scandinavia while the Saga of the People of Vatnsdal speaks of concubines.
And the archaeological evidence of the graves of Viking raiding parties also suggests that sailors were young males, rather than seasoned soldiers.
“Acquiring portable wealth seems to have been the major objective of raiding groups. Undefended monasteries away from settled areas would have been ideal targets,” added Prof Collard.
“By the end of the 8th century a number of regional polities and petty kingdoms had developed in Scandanavia.
“It is possible that the combined effects of polygyny, concubinage and social stratification simply reached a tipping point that led to a surge in raiding.
“With elite men monopolising an increasing percentage of women, many low-status men would have found it difficult to marry unless they were willing to engage in risky activites to improve wealth and status.”
The new paper was published in the journal Evolution & Human Behaviour.