Documentary: Secrets of the Viking Sword (2012)

This is the story of the Ulfberht sword.  This was the finest sword of the day, made with crucible steel.  The were used by the Vikings from 800 AD to 1000 AD.  No one in Europe could make this type of steel, with less slag and more carbon than usual during the day.  The high quality of steel, allowed to be more flexible and less likely to break.
The Vikings were known to trade with the Middle East, were an oven was discovered which would allow processing of steel at a high temperature, and thus help create crucible steel ingots.  The Viking use of this trade route corresponded with the period the swords were made.  It is quite an elaborate process to make the swords.  This video shows a blacksmith in Wisconsin reverse engineering the sword.  The swords are easily identified because the name is inlaid on the sword.  However, where they name came from no one knows.  It is speculated a bishop because there are a couple crosses in the name.  However the swords were only used by Vikings, and a small percentage of Vikings.
The last thing discovered in this show is the presence of knock-off Ulfberht swords.  These swords look like the real thing, and have the name forged in, but are not of the same high quality material.