According to this article on Tor.com, as many as half of Viking warriors may have been female.
Researchers at the University of Western Australia decided to revamp the way they studied Viking remains. Previously, researchers had misidentified skeletons as male simply because they were buried with their swords and shields. (Female remains were identified by their oval brooches, and not much else.) By studying osteological signs of gender within the bones themselves, researchers discovered that approximately half of the remains were actually female warriors, given a proper burial with their weapons.
The discovery was of misidentified female warriors, but I’d speculate that if warrior-duty was shared equally between the sexes, their society might have been more equal than we assume in other ways, too. How many of the skeletons with oval brooches were actually men?
What I find interesting here isn’t what it says about Vikings, but what it says about modern culture and how we view the past. We project our cultural norms backwards: fighting is a male job, so Vikings buried with swords must have been men. Or, we project our view of the recent past onto the more distant past: until recently fighting was exclusively a male job, so it always was. The issue is broader than gender roles: there are many ways that we can casually project their assumptions onto the past.
This is the kind of discovery that makes world-building in speculative fiction a delicate balancing act. If we mistakenly project our cultural norms onto the past, we’ll probably project them onto the future and onto secondary worlds as well. A well-realised future/imaginary society should be a mix of familiarity and strangeness: there are some universal truths of human nature, but there are other things that would be radically different from the world we know. The difficulty is working out which things are which. Discoveries like the female Viking warriors remind us that some things we put in the first category should actually go in the second.