The secrets behind the design and construction of the Vikings' Ulfberht sword, which was made between A.D. 800-1000, are revealed by master blacksmith Ric Furrer, who reverse engineers the sturdy weapon in the Season 40 premiere. Experts have also wondered where the high-carbon steel used in the blade came from, given that it wasn't used elsewhere in Europe at the time. Clues unearthed from Viking graves, however, point to an answer: traders who ventured to Persia or Afghanistan.