The boss is the iron dome at the centre of a shield, and it is the part that survives when the wood does not.What it is actually forA round shield has a hole cut through the middle so the hand can grip a bar behind it. The boss covers that hole. It protects the hand, it lets the shield be punched forward as a weapon, and it is the single most common Viking Age shield find because iron outlasts planking by a thousand years.Hand-forged in iron, ready to rivet to a shield.