The Vikings were among the fiercest warriors of all time. Yet only a select few carried the ultimate weapon of their era: the feared Ulfberht sword. Fashioned using a process that would remain unknown to the Vikings' rivals for centuries, the Ulfberht was a revolutionary high-tech tool as well as a work of art. Considered one of the greatest swords ever made, it remains a fearsome weapon more than a millennium after it last saw battle. But how did Viking sword makers design and build the Ulfberht, and what was its role in history? Now, NOVA uses cutting-edge science and old-fashioned detective work to reconstruct the Ulfberht and finally unravel the mystery of the Viking sword.