The Berserker Barracks are a military building from the High Middle Ages. The Berserker Barracks are available after having researched the Counterstrategy technology, and as the name would suggest, allow you to recruit Berserkers. It is recommended to get a Berserker Barracks because their stats are a huge 'step-up' from their predecessor, Mercenaries.
The berserker (also ulfhednar) were Viking warriors who fought naked, covered in fur. Went into battle under some trance, almost insensitive to pain, strong as bears or bulls psychotic profile, and came to biting their shields and no fire or steel that stop.
They threw themselves into battle with blind fury, even without armor or any protection, until the case has been heard that the water prematurely threw a drakkar and drowned and nothing could be done. His mere presence frightened his enemies and even his fellow soldiers, as in trance were unable to distinguish allies from enemies.