Lindisfarne Priory Stone, 794 C.E.
"From the fury of the Northmen, O lord, deliver us!," was the chant said to have been repeated endlessly in Dark Age churches and monasteries from northern Spain to France, west to Ireland (where the Vikings founded Dublin), Greenland, Iceland, and Vinland (Canada); the whole of the British Isles except the isolated southwestern tip, the Isle of Man, whence come the tailless manx cats, which are manx-allele positive, and north to Orkney, the Faroes and Shetland.
Around the Baltic periphery of Germany and Poland they came, and down the rivers of Ukraine and Russia to the Black Sea and Constantinople, where, unable to scale the massive walls and too impatient for sieges, some Vikings took up eating Spam and became mercenaries.
DNA analysis may have solved the puzzle, at least in the UK. Taking cheek-swab samples of hundreds of men around the British Isles and the northern islands, geneticists at University of London wanted to find out the echoes of how much "Viking" is left in the population today through the footprint of the Y chromosome.
In so doing, they hoped to learn more about two earlier population groups, the so-called 'Britons' or Celts and the Angles and Saxons, tribes which started invading Angle-land (German) as early as 300 C.E., best remembered in the old English tale of Beowulf, a time of magic swords, rings, dragons, and monsters.
Were they just raiding parties, or did they settle in these areas? The king of France, tired of their incessant pillaging and vandalism, made an accommodation with Rollo, a Viking war leader, by giving him a large hereditary fief, Normandy. In return, Rollo was supposed to settle down, support the king, and most importantly, defend the coast against other Vikings. Vikings later settled in southern Italy/Sicily, Russia-playing a role in the founding of the state, and around Constantinople.
The gene analysis was supported by the BBC and presented in a BBC Learning Series, the 'Blood of the Vikings.' It is no longer posted but may appear again. The accompanying scientific publication info is here. Additional research has just been completed.
The results were quite interesting.
The Vikings that invaded the British Isles were primarily from two points of origin, Denmark and Norway, who exhibited some genetic differences. It turns out that the early population of Britain has partial affinity with the pre-bronze age Gallic peoples that inhabited a broad swath of land from Asia Minor across Europe to France and Spain, in particular the Basques.
For a time prior to 6,000 B.C.E., the English channel was a misty meadow or tidal valley, forming a land bridge with the continent. This native Briton population is echoed in the genetics of southwest Britain and central Ireland, which resisted the Angles, Saxons, Vikings, and Normans, and is still (21st century) not fully assimilated with the other parts of the British Isles, according to geneticists.
left: Genetic footprint of UK populations in the 21st century
right: The approximate extent of Old Norse and related languages in the early 10th century around the North Sea. The red area is the distribution of the dialect Old West Norse, the orange area is the spread of the dialect Old East Norse and the green area is the extent of the other Germanic languages with which Old Norse still retained some mutual intelligibility
While there is a visible genetic difference between these remote, early peoples who were isolated by geography, and the Angles and Saxons who occur throughout the remainder of England; there was an insignificant genetic difference between the Anglo-Saxons and the Danish Vikings, mainly because these tribal groups all originated in the same area, northern coastal Europe.
In fact, accounts and the archaeology of the Saxon invasions tell us that their raids were somewhat like the Viking raids 400 years later. Groups of warriors arrived by sea in boats festooned with shields. In response, the Romans created a military office to defend against these raiders, the Count of the Saxon Shore (Comes Litoris Saxonorum), who built a chain of stone fortifications along the coast to defend against the raiders and safeguard in-kind taxes.
Walls of Garrianonum fort
At least one pretender to the imperial throne, Carausius, held this office prior to seizing power and creating a Britanno-Gallic empire, so we may conclude that it was an important administrative post with ample resources. The last legions sailed away from Britain in 410 C.E. to take part in a campaign on the continent, never to return, leaving the Romanized Briton population to deal with the seafaring Saxons and Angles.
Interestingly, genetic differences occur fairly dramatically in the North Sea isles held by Britain, the north of Scotland, and parts of the coast of Western England and Ireland, where the genetic footprint of the Norwegians is evident, with some 40-60% of the population showing affinity to that of Norway in the northern islands, and pockets elsewhere.
In the U.S., you would have to go to North Dakota to see anywhere near a similar level of Norwegian ancestry, which is around 30% of the population, 17% in Minnesota and 14% in South Dakota.