One contingent of these people were defeated by the Earl of Orkney at the B
One contingent of these people were defeated by the Earl of Orkney at the Battle of Clontarf. A leader of these people descended from Mieszko I of Poland and won the Battle of the Holy River, although he'd later face a rebellion from his regent, Ulf Jarl. Prominent warriors among these people were called beserkers. For 10 points, name these seafaring people who launched numerous invasions of Europe during the Middle Ages.
One contingent of these people were defeated by the Earl of Orkney at the Battle of Clontarf.
{Vikings} [or {Norsemen}; or {Northmen}]