Archaeologists are trying to link the find to historical events
Fifty-one decapitated skeletons found in a burial pit in Dorset were those of Scandinavian Vikings, scientists say.
Mystery has surrounded the identity of the group since they were discovered at Ridgeway Hill, near Weymouth, in June.
Analysis of teeth from 10 of the men revealed they had grown up in countries with a colder climate than Britain's.
Archaeologists from Oxford believe the men were probably executed by local Anglo Saxons in front of an audience sometime between AD 910 and AD 1030.
The Anglo Saxons were increasingly falling victim to Viking raids and eventually the country was ruled by a Danish king.
The mass grave is one of the largest examples of executed foreigners buried in one spot.
It was discovered during investigative excavation work before construction started on a controversial £87m relief road through the ridgeway.
Samples of 10 remains were identified as Scandinavian by Dr Jane Evans and Carolyn Chenery, of NERC Isotope Geosciences Laboratory, part of the British Geological Survey, based in Nottingham.
Their work has revealed that the men had scattered Scandinavian origins, with one even thought to be from north of the Arctic Circle.
Isotopes in the men's teeth also show they had eaten a high protein diet, comparable with known sites in Sweden.
Initially, it was thought the burial site dated from the Iron Age (from 800 BC) to early Roman times (from AD 43) after examining pottery in the pit, later identified as a Roman quarry.
Isotope testing was carried out on the men's teeth
Radiocarbon dating later revealed they were from the Saxon period.
Oxford Archaeology removed the 51 skulls from the ground and are continuing to examine the remains to try to link the find to historical events.
Project manager David Score said: "To find out that the young men executed were Vikings is a thrilling development.
"Any mass grave is a relatively rare find, but to find one on this scale, from this period of history, is extremely unusual."
He added that without analysing all the bodies it was impossible to know for certain that all the skeletons were those of Vikings, but it was possible to make a "strong inference".
The archaeologists believe the men were stripped naked either before being killed, or before being buried, because there was no evidence of clothing, such as pins or toggles.
Most of them were in their late teens to early 20s, with a handful in their 30s.