Eight of the 16 residents of the Swedish city of Sigtuna, who lived in the Viking Age and whose remains were analyzed by the researchers, turned out to be visitors, is told in Current Biology . Some of them were “near” migrants and came from other regions of Scandinavia, while others grew in the territory of modern Lithuania, Ukraine and the British Isles. Two people turned out to be immigrants in the second generation.
The Viking Age is called the period from the 8th to the 11th century, when Scandinavians established trade relations with other European states, and often conquered and plundered them; settled Iceland and Greenland and reached North America. At this time in Scandinavia itself there were cities, some of which exist today. The oldest of them was the town of Sigtuna, which is located on the shore of Lake Malaren, connected with the Baltic Sea, and now enters the conglomeration of Stockholm. Presumably, the city was founded at the end of X century and for 250 years was one of the most important political, commercial and religious centers. In the city there was a royal residence and here around the 990s the first Swedish coinage was minted. At the end of the XII century, the city was plundered by Baltic pirates, which probably appeared from the territory of modern Karelia, Latvia and Estonia. Nevertheless, life in the city did not stop. Sigtuna lost its importance in the XIII century, when as a result of the post-glacial rise of the land, navigable routes to the city became shallow.
In the heyday of the city there were several Christian cemeteries. They proved to be an important find not only for archaeologists, but also for geneticists. Unlike Christians, the Gentile Vikings most often burned their dead, so it was impossible to extract DNA from their remains. In Christian cemeteries remains were preserved, whose DNA could be isolated and analyzed. The researchers, led by Anna Kjellström of the University of Stockholm, decided to try to understand how mobile the inhabitants of Sigtuna were. The fact that Scandinavian people traveled through Europe in the Middle Ages was well known to scientists , but it was not clear how many Europeans came to Scandinavia.
To find this out, researchers isolated DNA from the remains of 23 people (16 men and nine women) who lived in the X-XII centuries, and cut out the complete sequences of their genomes. As a reference, scientists used sequences of genomes from representatives of 21 European populations and 13 Europeans who lived in the Middle Ages on the territory of modern England, Sweden, Hungary and Montenegro. In addition, in the enamel of 16 of them, scientists determined the ratio of strontium isotopes. But only “isotopic signature” of strontium was found in the remains of 15 more people. Strontium serves as a good marker of human mobility. Its isotopes accumulate in the human enamel during the period of its formation and by their ratio it is possible to determine where it grew.
Genetic data showed that some of the 23 people came to Sigtuna from other regions of Scandinavia, and part from afar – from the British Isles, the territory of modern Lithuania, Ukraine, northern Germany, and from northern Russia. Half of the city’s residents, who managed to determine both the “isotopic signature” and the sequence of the genome, turned out to be visitors. Some of them were immigrants in the second generation – the ratio of isotopes in them was local, and they were genetically related to other populations. Judging only by the isotope signature, 70 percent of women and 44 percent of men came to Sigtuna from other places.
Previously, the researchers found that the Vikings were engaged in sea trade as early as the beginning of the VIII century, several decades before the raids on other European states. Presumably, they gained navigational skills, which were then useful to them for raids.