It was described by some arab chronicle writer in Hedeby... >>reaserching<<
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Ibrahim ibn Yaqub al-Tartushi (thank gods for copying D:) - Check "lifestyle" paragraph in
this article.
And Stara Baśń had plenty of terrible historical mistakes, yet it's one of the best reconstructions (the vikings are actual reenactemnt group from Poland - Jomsborg vikings that I drank many horns of mead with)

And, it's a legend, not historical movie, so horns, leather lamellars and square shields are acceptable.