Video: Medieval Viking Ulfberht swords are some of the most famous swords in history because they were so obscenely strong that it's almost unbelievable that bladesmiths in the 9th century were even able to make them. Made from crucible steel, the swords stood out from everything from that time period. Hell, the process of forging these Ulfberht swords is so difficult that even modern bladesmiths have trouble getting the sword right.