The Vikings, that is the VI Kings or 6 Kings (i.e. six roman rulers).
sixers
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Vikings....Roman numeral for 6 is VI and Kings are rulers
Bills.
The Arizona Cardinals.
Minnesota Vikings
real madrid
Houston Oilers
Because someone thought it would make a cool team name.
They were usually made by a team of Roman soldiers.
I believe that since we are talking about 1 group (singular) the correct way to say this would be 'A group of horses is called a team'.