(This program is no longer available for online streaming.) 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 "Secrets of the Viking Sword."