#6: Battle of Stamford Bridge – Norse–English Conflict (1066)
During the Battle of Stamford Bridge in 1066, English forces clashed with Viking troops under Harald Hardrada. In the chaos, English soldiers fired volleys of arrows at shapes they thought were enemy fighters, only to hit some of their own advancing men.
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The bridge and surrounding fields were crowded, visibility was poor, and units mixed together as they pushed forward. Several English troops were struck by friendly arrows before commanders managed to regroup everyone. The battle still ended in an English victory, but confusion cost lives.