Hmmm... inaccuracies between the show and the vikings. As far as for the battlefield, the most glaring inaccuracy is their armor, or lack-thereof. In the show, they seem to be more armored in the fashion of the Celts. The Celts were known to run screaming into battle pretty much nekid, and quite successfully as like wild berserkrs.
In the show, they are even less armored than the Romans, which were armored well in the front (girth hoops), used shields, but were nekid at the back. Vikings would wear heavy padding or if affordable (or looted) they would wear chain. But they shared a bit of tactics with the Romans nonetheless, however a little more armored in general on the retreat side of things.
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First shield on the left...
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