Dr Tarrin Wills, from the Centre for Scandinavian Studies, believes that Vikings used their understanding of human psychology to "profile" possible trouble-makers. He recently presented his research at the British Science Festival.
Wills studied period literature and learned that "authors pinpointed physical characteristics of high testosterone levels – known to cause violent behaviour – creating some of the earliest 'criminal mugshots'." He added, "What can be seen by examining the literature is that those who recorded the sagas realised that physical features were significant when it came to those most likely to behave in violent ways. It seems they were sensitive not only to anti-social behaviour – everything from insults to homicide - but found ways of understanding the biological relationship to that behaviour."